2024-03-28T22:02:29Zhttps://www.repo.uni-hannover.de/oai/requestoai:www.repo.uni-hannover.de:123456789/7692022-12-02T19:35:27Zcom_123456789_11col_123456789_14doc-type:Articledoc-type:Textopen_accessddc:530status-type:publishedVersion
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Malobabic, Sina
author
Jupé, Marco
author
Ristau, Detlev
author
2016
Cloud computing is a paradigm in which information is permanently stored in servers on the Internet and cached temporarily on clients. Virtual private network (VPN) is the most widely used technology for secure cloud access. Unfortunately, VPN-based cloud services become unavailable when a VPN failure occurs. In this paper, we propose a new scheme to improve the availability of VPN connections against such failures, called high-availability virtual communication (HAVC). Unlike most of the multipath transmission schemes in the literature, the proposed scheme is implemented by using a virtualization technique, and its protocol functions are independent of existing networks - potential clients are not required to modify their applications or operating systems. Simulation results show that the HAVC can not only tolerate VPN failures but also achieve high transmission performance.
Malobabic, Sina; Jupé, Marco; Ristau, Detlev: Spatial separation effects in a guiding procedure in a modified ion-beam-sputtering process. In: Light: Science and Applications 5 (2016), e16044. DOI: http://dx.doi.org/10.1038/lsa.2016.44
http://www.repo.uni-hannover.de/handle/123456789/769
http://dx.doi.org/10.15488/745
EM field separation
ion beam sputtering
plasma guiding
Coatings
Deposition
Ion sources
Refractive index
Sputtering
EM field
High reflection mirrors
Ion-beam sputtering
Mechanical components
Mechanical movements
Particle contamination
Spatial separation
State of the art
Ion beams
Spatial separation effects in a guiding procedure in a modified ion-beam-sputtering process
oai:www.repo.uni-hannover.de:123456789/34482022-12-02T08:02:55Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
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Posso Trujillo, Katerine
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2018
In dieser Arbeit werden quantenentartete Gemische auf ihre Eigenschaften als Quellen für Präzisionsatominterferometer zum Test des Einsteinschen Äquivalenzprinzips untersucht. Um die notwendige Auflösung zu erreichen, sollen die Interferometriezyklen auf mehrere Sekunden ausgedehnt werden. Die bekannten Hauptbeiträge an systematischen Effekten, die bei realistischen Aufbauten auftreten, sind hierbei berücksichtigt, und für einige werden Strategien zur Unterdrückung präsentiert. Die Gemische die hier betrachtet werden, sind Bose-Einstein-Kondensate aus 87Rb/85Rb und 87Rb/41K. Eine simultane Absenkung der Expansionsraten beider Komponenten in den Temperaturbereich von weniger als 100 pK ist notwendig, um einerseits freie Entwicklungszeiten der Kondensate von 10 s zu ermöglichen, und andererseits systematische Fehler zum Beispiel verursacht durch die atomare Bewegung in den Wellenfronten der Lichtfelder zu unterdrücken. Um diese Anforderungen erfüllen zu könnnen, wurde die Rolle der Wechselwirkung der Teilchen untereinander betrachtet, die von ihrer einfachen Durchstimmbarkeit mit Hilfe von Feshbach-Resonanzen profitiert. Neben der Manipulierbarkeit der Wechselwirkung wurden Delta-Kicks zur Kollimation untersucht, durch die der Einfluss der führenden systematischen Fehler unterdrückt wird. Neben dem oben genannten Gemisch wurden auch die Gemische 87Rb/39K und 87Rb/170Yb untersucht. Das 87Rb/87K-Gemisch wurde als Kandidat für Hochpräzisionsatominterferomtrie in Mikrogravitation identifiziert. Das Yb-basierte Gemisch hat den vorteil, dass die Wechselwirklung ohne zusätzliche Feshbachfelder durchgeführt werden kann. Für die Delta-Kicks wurde eine Vielzahl an Fallengeometrien untersucht, wie etwa die Dipolfalle, chip-basierte Potentiale, sowie das TOP-Fallenpotential (engl.: Time-Orbiting-Potential), um Majorana-Verluste zu verhindern. Die Berechnungen wurden mit Hilfe der Gross Pitaevskii Gleichung und Skalierungstheorie vorgenommen.
Posso Trujillo, Katerine: Theoretical study of the preparation of quantum degenerate mixtures for precision atom interferometry. Hannover : Gottfried Wilhelm Leibniz Universität, Diss., 2015, iii, 121 S. DOI: https://doi.org/10.15488/3418
http://www.repo.uni-hannover.de/handle/123456789/3448
http://dx.doi.org/10.15488/3418
BEC mixtures
Delta kick cooling
Equivalence principle tests
atom interferometry
Delta-kick-Kühlung
STE-QUEST
Äquivalenzprinzip Tests
Atominterferometrie
Theoretical study of the preparation of quantum degenerate mixtures for precision atom interferometry
oai:www.repo.uni-hannover.de:123456789/35102022-12-02T08:02:55Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
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Grotti, Jacopo
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2018
This work presents the first measurement campaigns performed with PTB transportable optical lattice clock based on Strontium atoms for applications in clock comparisons and relativistic geodesy.
Grotti, Jacopo: A transportable optical lattice clock for metrology and geodesy. Hannover : Gottfried Wilhelm Leibniz Universität, Diss., 2018, viii, 131 S. DOI: https://doi.org/10.15488/3480
http://www.repo.uni-hannover.de/handle/123456789/3510
http://dx.doi.org/10.15488/3480
Transportable Optical Clock
metrology
Relativistic Geodesy
frequency standards
Chronometric leveling
Transportable Optische Gitteruhr
Metrologie
Relativistische Geodesie
Frequenzstandards
Chronometrisches Nivellement
Strontium
A transportable optical lattice clock for metrology and geodesy
oai:www.repo.uni-hannover.de:123456789/35412022-12-02T08:02:55Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
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Brause, Nils Christopher
author
2018
The Laser Interferometer Space Antenna (LISA) is a planned gravitational wave detector to be positioned in space. It consists of three spacecrafts that use Long Range Interferometry (LRI) to measure relative distance changes between them. An important component of LISA is the LISA Metrology System (LMS) which is responsible for the distance measurements as well as various auxiliary functions: The beatnote acquisition allows the LMS to lock to an incoming beatnote signal with an unknown frequency and amplitude. It measures both with a Fast FourierbTransform (FFT) and controls the starting frequencies and gains of the Digital Phase Locked Loops (DPLLs) accordingly. The laser locking algorithm is used to lock the frequency of one laser to the frequency of another laser. This is done by locking the difference frequency between two lasers to a constant target and thus enabling heterodyne interferometry. The amplitude of the incoming beatnote signal can vary greatly over time. To compensate for that, the Automatic Gain Control (AGC) functionality observes the amplitudes and reconfigures the gains of the DPLLs accordingly. In LISA the pointing will be measured using an advanced Differential Wavefront Sensing (DWS) scheme, which track the differential phases between the segments of a Quadrant Photo Diode (QPD) directly instead of calculating them from the measured phases of the segment DPLLs. This improves the Carrier to Noise Density Ratio (CNR) in the DPLLs by a factor of two. The absolute distance between the spacecrafts is also measured to enable Time-Delay Interferometry (TDI) in post-processing. This is done by sending a Pseudo-Random Noise (PRN) code via the laser link to a distant spacecraft, where it is correlated with a local copy of the same PRN code to determine the travel distance from the measured delay. Since only one of the three LISA spacecrafts has a radio link to earth, data has to be transferred between the three spacecrafts. This functionality is part of the Delay Locked Loop (DLL), by modulating the data onto the PRN code. In the course of this thesis, all the necessary auxiliary functions will be developed, thoroughly described and measured.
Die Laser Interferometer Space Antenna (LISA) ist ein geplanter Gravitationswellendetektor, der im Weltraum stationiert werden soll. Sie besteht aus drei Satelliten, die Long Range Interferometry (LRI) nutzen um relative Abstandsänderungen zwischen ihnen zu messen. Eine wichtige Komponente von LISA ist das LISA Metrology System (LMS), welches für die Abstandsmessungen sowie diverse Hilfsfunktionen zuständig ist: Die Beatnote Acquisition ermöglicht dem LMS sich auf eine eingehende Beatnote unbekannter Frequenz und Amplitude zu locken. Sie misst beides mit einer Fast Fourier Transform (FFT) und kontrolliert damit die Startfrequenz und Gains der Digital Phase Locked Loops (DPLLs). Der Laser Lock Algorithmus wird benutzt um die Frequenz eines Lasers auf die eines anderen zu stabilisieren. Dies wird erreicht indem der Frequenzunterschied beider Laser konstant gehalten wird, wodurch Heterodyninterferometrie ermöglicht wird. Die Amplitude des Eingangssignals variiert stark im Laufe der Zeit. Um dem entgegenzuwirken folgt der Automatic Gain Control (AGC) der Amplitude und passt die Gains der DPLLs laufend an. In LISA wird die Richtung der Laserstrahlen mit Hilfe eines weiterentwickelten Differential Wavefront Sensing (DWS) Schemas gemessen, das die differentiellen Phasen zwischen den Segmenten der Quadrant Photo Diode (QPD) direkt misst. Dies verbessert die Carrier to Noise Density Ratio (CNR) in den DPLLs um einen Faktor 2. Der absolute Abstand zwischen den Satelliten wird ebenfalls gemessen um im Postprocessing Time-Delay Interferometry (TDI) zu ermöglichen. Dies wird erreicht indem ein Pseudo Random Noise (PRN) Code über die Laserverbindung zu einem entfernten Satelliten geschickt wird, wo er mit einer lokalen Version davon korreliert und so die Entfernung aus der gemessenen Verzögerung berechnet wird. Da nur einer der drei LISA Satelliten eine Funkverbindung zur Erde hat, müssen die Daten zwischen den Satelliten transferiert werden. Diese Funktionalität ist Teil der Delay Locked Loop (DLL), indem die Daten auf den PRN Code aufmoduliert werden. Im Laufe dieser Doktorarbeit werden alle nötigen Hilfsfunktionen entwickelt, vollständig vorgestellt und vermessen.
Brause, Nils Christopher: Auxiliary function development for the LISA metrology system. Hannover : Gottfried Wilhelm Leibniz Universität, Diss., 2018, XV, 186 S. DOI: https://doi.org/10.15488/3511
http://www.repo.uni-hannover.de:8080/handle/123456789/3541
http://dx.doi.org/10.15488/3511
interferometry
metrology
auxiliary functions
Interferometrie
Messtechnik
Hilfsfunktionen
Auxiliary function development for the LISA metrology system
oai:www.repo.uni-hannover.de:123456789/35562022-12-02T08:02:55Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
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Isleif, Katharina-Sophie
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2018
The development and investigation of laser interferometry concepts for performing precise length measurements at frequencies below 1Hz is the main topic of this thesis. These concepts are quintessential for space-based measurements of gravitational waves or the Earth gravity field. For the Laser Interferometer Space Antenna (LISA) and future satellite geodesy missions, various interferometer types have been studied between 2014 and 2018 at the Albert Einstein Institute (AEI) in Hannover as a part of the work presented here. The first part of this thesis presents conceptual design studies of phase reference distribution systems (PRDSs) for LISA. The usage of Telescope Pointing is the baseline mechanism for the current LISA design and implies the need for a light-exchanging backlink connection between two rotating optical benches within one satellite. Different backlink implementations are presented and analyzed, the final choice however remains one of the last open questions for the LISA optical metrology. A test-bed for comparing three backlinks with each other in a single, so-called Three-Backlink interferometer (TBI) experiment, has been simulated and a detailed noise estimation, including a critical stray light analysis, is presented. A free-beam connection between two moving set-ups was established by which the full functionality of the experimental environment was validated. The design of the TBI has been completed and the experiment, consisting of two rotating quasi-monolithic optical benches, is currently under construction. The full experiment will enable to test the performance of LISA backlink candidates with a precision of 1 pm/√Hz in a relevant environment. The second part of this thesis describes alternative interferometer techniques for reducing the complexity of optical set-ups, while modern digital signal processing is applied for recovering the desired phase information. The simplifications in the optical part enables multi-channel operation and multi-degree of freedom readout, which is required for future gradiometers in satellites consisting of six or more test masses. An experiment simulating such a test mass readout with only a single optical component has been established. Interferometric readout noise levels of 1.0pm/√Hz at 100mHz were achieved by using deep frequency modulation interferometry (DFMI), a novel technique developed as part of this thesis.
Die Entwicklung von Laserinterferometern für präzise Längenänderungsmessungen im 1mHz-Frequenzbereich ist das Kernthema dieser Arbeit. Diese finden Anwendung in der Detektion von Gravitationswellen und der Messung des Erdschwerefeldes aus dem Weltraum. Verschiedene Interferometerkonzepte wurden für die Laser Interferometer Space Antenna (LISA)- und zukünftige geodätische Missionen innerhalb der hier dargestellten Arbeit am Albert-Einstein-Institut (AEI) in Hannover zwischen 2014 und 2018 untersucht. Der erste Teil dieser Arbeit befasst sich mit einer Designstudie über unterschiedliche Phasenreferenzverteilungssysteme (PRDSs) für LISA. Das derzeitige Design sieht das sogenannte Telescope Pointing als Basis-Mechanismus vor, wodurch eine Backlink-Verbindung zwischen zwei rotierenden optischen Bänken innerhalb eines Satelliten benötigt wird. Die Laser werden hiermit zwischen den beiden Interferometern ausgetauscht. Eine konkrete Realisierung dieses Backlinks ist eine der letzten offenen Fragen für das optische Design von LISA. Das sogenannte Drei-Backlink Interferometer (TBI) wurde speziell entworfen und dient als Testumgebung, in welcher drei Backlinks in einem einzelnen Aufbau miteinander verglichen werden. Optische Simulationen und eine Vorhersage möglicher Rauschquellen werden in dieser Arbeit präsentiert. Eine Freistrahl-Verbindung zwischen zwei rotierenden Bänken wurde bereits untersucht und es konnte gezeigt werden, dass die experimentelle Infrastruktur voll funktionsfähig ist. Das Design des Drei-Backlink Experiments ist abgeschlossen und es wird derzeit konstruiert. Der zweite Teil dieser Arbeit beschreibt alternative Interferometertechniken um die Komplexität optischer Aufbauten zu reduzieren. Moderne digitale Verarbeitungssysteme werden benutzt, um die gewünschte Phaseninformation zurückzugewinnen. Eine Vereinfachung der Optik ermöglicht den Betrieb mehrerer Kanäle gleichzeitig und die Auslesung vieler Freiheitsgrade. Diese Techniken werden in zukünftigen Satelliten-Gradiometern benötigt, um die Bewegung mehrerer Testmassen zu bestimmen. Dies wurde in einem optischen Aufbau mit nur einer einzelnen optischen Komponente simuliert. Mit tiefen Laserfrequenzmodulationen (DFMI), einer im Rahmen dieser Arbeit entwickelten Methode, konnte eine Messgenauigkeit von unter 1.0 pm/√Hz bei 100mHz erreicht werden.
Isleif, Katharina-Sophie: Laser interferometry for LISA and satellite geodesy missions. Hannover : Gottfried Wilhelm Leibniz Universität, Diss., 2018, xxvii, 241 S. DOI: https://doi.org/10.15488/3526
https://www.repo.uni-hannover.de:443/handle/123456789/3556
http://dx.doi.org/10.15488/3526
gravitational physics
laser interferometry
space application
Gravitationsphysik
Laserinterferometrie
Weltraumanwendung
Laser interferometry for LISA and satellite geodesy missions
oai:www.repo.uni-hannover.de:123456789/36962022-12-02T08:02:55Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
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Lange, Karsten
author
2018
The predictions of quantum mechanics often differ from our everyday experiences. In the classical case, the state of a system can be predicted precisely, assuming the exact knowledge of all parameters. This is not possible in quantum mechanics. For example, the spin of one particle can be simultaneously in two different states, until a measurement defines the actual state. If multiple particles are in such superposition states, their spins can be coupled with each other such that the measurement of one particle changes the physical state of the other particles. This coupling effect is a fundamental part of quantum mechanics and is called entanglement. It is a central requirement for applications in the fields of quantum communication, quantum cryptography and quantum computing. One possibility to create entanglement are spin-changing collisions in a spinor Bose-Einstein condensate. These collisions are described by a nonlinear process, which creates non-classical correlations between all atoms of the Bose-Einstein condensate. Within this thesis, 87Rb spinor Bose-Einstein condensates are used to demonstrate Einstein-Podolsky-Rosen entanglement by the generation and analysis of a two-mode entangled state in spin space [A1]. These states are applied in an interferometric measurement with a resolution of 2.05+0.34 -0.37 dB beyond the standard quantum limit [A2]. Depending on the dynamics, the process can also be analogous to the dynamical Casimir effect [A3]. The entanglement between the particles in these publications is strongly connected with their indistinguishability. It is thus possible to make the particles distinguishable again and recover the entanglement between the now separated particles? This question is approached by cutting an entangled state of indistinguishable particles into two spatially separated atomic modes - creating a two-mode entangled state in real space. As shown in Ref. [A4], the entanglement between the two separated clouds of a Bose-Einstein condensate can be measured directly. In the future, the created state can be employed for a test of quantum nonlocality.
Lange, Karsten: Two-mode entanglement in spin and spatial degrees of freedom. Hannover : Gottfried Wilhelm Leibniz Universität, Diss., 2018. 23 S. DOI: https://doi.org/10.15488/3664
https://www.repo.uni-hannover.de/handle/123456789/3696
http://dx.doi.org/10.15488/3664
Bose-Einstein condensate
spin dynamics
entanglement
Bose-Einstein-Kondensat
Spindynamik
Verschränkung
Two-mode entanglement in spin and spatial degrees of freedom
oai:www.repo.uni-hannover.de:123456789/37222022-12-02T08:02:55Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
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Popp, Manuel André
author
2018
Quantum sensors based on atomic interferometry are becoming valued tools for precision measurements in various research areas such as metrology, Earth sciences and inertial sensors. However, the verification of their accuracy is linked to the resolution and thus the free-fall time of the interferometer, which can only be extended on Earth by levitation or other methods, which themselves usually result in a loss of accuracy. Especially in the field of basic research, space-based measurement apparatuses are therefore fascinating prospects to set new standards for fundamental tests and measurements in Earth observation. In space, it is possible to drop the measuring devices alongside their test objects as long as desired, which allows a considerable extension of interferometry time. An important prerequisite for interferometry on such long time scales is the minimization of propagation velocity and initial expansion, which can only be achieved with ultra-cold atomic ensembles such as a bose-einstein condensate (BEC). Therefore, the creation of such a BEC on a compact, space-based platform represents a central challenge for the feasibility of atom interferometers in space. An important step for the necessary adaptation of existing laboratory equipment to space platforms is the sounding rocket mission maius-1, which is to develop and test both technology and methodology for the use of quantum sensors in space. The core of the scientific payload of maius-1 is an ultra-compact cold atomic source, based on the atom chip technology, employed to generate BEC in magnetic traps. The precise magnetic field control with atomic chips, in an environment like that of a sounding rocket, requires specialized current drivers that combine ruggedness, compactness and excellent noise performance that is yet unattainable with commercial technology. This thesis presents design and characterization of a new generation of compact current drivers for this purpose. Based on a typical preparation of a BEC, core specifications for current drivers are derived and their effects on the experiment are discussed. These specifications are then supplemented by the technical requirements of a sounding rocket. The evaluation of the requirements catalogue results in three current driver designs. First of all, an analog, flexible prototype is presented, which, in addition to the demonstration of miniaturization and high power densities, allows many possible settings of control parameters and has been used in the evaluation phase of the maius-1 atomic chip section. The experiences from this phase flowed into the designs of the maius flight hardware, which offer two architectures, adapted to the given technical conditions: one model for the employment at atom chips and one model to drive the external coils around the atom chip. The design process was supported by detailed circuit simulation. They enable fast optimization of control architecture and parameters for any load. Particularly in the case of coils, which are of crucial importance for magnetic traps, the prediction quality obtained represents a major technological advantage in terms of optimizing switching behavior, since predecessor experiments previously depended on heuristic methods for this task. With a volume reduction of more than one order of magnitude compared to laboratory electronics, and output currents of up to 10 A, the current driver modules of maius can be used under harsh temperature conditions from 10 to 70 ℃. They show a temperature drift of 100 ppm/K (chip) or 32 ppm/K (coils). In thermal equilibrium, the drivers work with a relative current stability of 3⋅10−5 (chip) and 5⋅10−6 (coils). Technical current noise is a decisive limitation of the lifetimes in magnetic atom traps. Thus, the noise characteristics of the designs are evaluated in a spectral analysis and compared with commercial laboratory equipment from previous experiments. The thereby obtained values for the integrated current noise of 108 μARMS (Chip) and 64 μARMS (Coils) (1Hz-99.8 kHz), represent an improvement by a factor of 3.8, or 6.4 in comparison to the commercial reference. To conclude the first characterization of the developed designs before the launch of maius the first operational measurements of the integrated source of cold atoms are presented and evaluated in view of temperature drift of the current driver modules in the experiment. The achieved performance values set a new benchmark in the field of compactification and noise performance and thus provide a key technology for compact, atomic chip-based quantum sensors. The presented designs operated successfully on the maius-1 mission which on January 23rd, 2017, among other things, could demonstrate the first creation of a BEC in space.
Popp, Manuel André: Compact, low-noise current drivers for quantum sensors with atom chips. Hannover : Gottfried Wilhelm Leibniz Universität, Diss., 2018, XIV, 166 S. DOI: https://doi.org/10.15488/3688
https://www.repo.uni-hannover.de/handle/123456789/3722
http://dx.doi.org/10.15488/3688
current control
atom chips
Bose-Einstein condensate
Stromregelung
Atomchips
Bose-Einstein-Kondensat
Compact, low-noise current drivers for quantum sensors with atom chips
oai:www.repo.uni-hannover.de:123456789/37392022-12-02T08:02:55Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
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Hannig, Stephan
author
2018
At the time of writing, state of the art stationary optical clocks reach 10 −18 sys- tematic fractional frequency uncertainty, which allows for the search of new physics beyond the standard model and lays the foundation for new applications such as chronometric leveling, where height differences relative to the geoid are derived from frequency comparisons among optical clocks. Transportable optical clocks allow for chronometric leveling between distant lo- cations which are not connected by a direct line of sight but via length stabilized optical fiber. Moreover, they facilitate frequency comparisons between distant sta- tionary clocks via subsequent side-by-side comparisons without the necessity of a long-range fiber connection. A transportable optical clock employing a single 40Ca+ ion has been reported and a neutral atom 87Sr lattice clock has been employed in a chronometric leveling campaign. However, these clocks report an estimated systematic fractional frequency uncertainty in the high 10^−17 range, which limits their height resolution to a level of approximately 1 m. 27Al+ has one of the smallest blackbody radiation shifts, small linear and quadratic Zeeman shifts and a negligible quadrupole shift, which makes it a candidate for a highly accurate optical clock. This thesis reports on the development, set-up, and characterization of a transportable 27Al+ clock setup with 40Ca+ as logic ion. The setup is simple, modular, compact, and mechanically stable. Ions of both species are generated via pulsed laser ablation and subsequent photoionization. They are confined in a multi-layer trap with segmented loading and experiment zones. Using a single 40Ca+ ion as probe, heating rates of below 10 quanta per second have been measured in all three directions for trap frequencies around 2π × 2 MHz, and pulsed sideband cooling to mean motional quantum numbers below 0.1 quanta was demonstrated. Imaging close to the diffraction limit with a signal to noise ratio of 800 for 300 ms exposure time on a sCMOS camera was achieved using a single NA = 0.51 biaspheric lens. Simultaneously, a state discrimination error below 10^−5 in 100 µs was obtained using a PMT. From the excess micromotion second order Doppler shift, secular motion second order Doppler shift, BBR shift, and background gas collision shift, a partial systematic fractional frequency uncertainty of 1.7 × 10^−18 was inferred, which is equivalent to a height resolution of ca. 2 cm. Moreover, a highly stable mechanical monolithic enhancement cavity for SHG has been developed and demonstrated to withstand accelerations of 3 g rms for 30 min. It has been operated for an uninterrupted period of 130 h without decay in output power in the mid-UV due to O2 -purging, its sealed design, and material selection, which solves the often observed crystal degradation in UV applications. The cavity has been employed in the 27Al+ logic laser system. In conclusion, it has been shown that an 27Al+ ion quantum logic optical clock operated in the present transportable setup could reach an estimated systematic fractional frequency uncertainty of 1.7 × 10^−18 , provided that all other shifts, such as the second order Zeeman shift, are negligible. This paves the way towards chronometric leveling with an unprecedented height resolution of about 2 cm.
Hannig, Stephan: Development and characterization of a transportable aluminum ion quantum logic optical clock setup. Hannover : Gottfried Wilhelm Leibniz Universität, Diss., 2018, 11, 7, 152 S. DOI: https://doi.org/10.15488/3705
https://www.repo.uni-hannover.de/handle/123456789/3739
http://dx.doi.org/10.15488/3705
Transportable 27Al+ Ionenuhr
hochstabile Verdopplungsresonatoren
Development and characterization of a transportable aluminum ion quantum logic optical clock setup
oai:www.repo.uni-hannover.de:123456789/38062022-12-02T15:12:30Zcom_123456789_1com_123456789_11col_123456789_7col_123456789_14doc-type:Articledoc-type:Textopen_accessddc:530status-type:publishedVersion
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Brennecke, Simon
author
Lein, Manfred
author
2018
Photoelectron momentum distributions from strong-field ionization are calculated by numerical solution of the one-electron time-dependent Schrödinger equation for a model atom including effects beyond the electric dipole approximation. We focus on the high-energy electrons from rescattering and analyze their momentum component along the field propagation direction. We show that the boundary of the calculated momentum distribution is deformed in accordance with the classical three-step model including the beyond-dipole Lorentz force. In addition, the momentum distribution exhibits an asymmetry in the signal strengths of electrons emitted in the forward/backward directions. Taken together, the two non-dipole effects give rise to a considerable average forward momentum component of the order of 0.1 a.u. for realistic laser parameters.
Brennecke, S.; Lein, M.: High-order above-threshold ionization beyond the electric dipole approximation. In: Journal of Physics B: Atomic, Molecular and Optical Physics 51 (2018), Nr. 9, 94005. DOI: https://doi.org/10.1088/1361-6455/aab91f
https://www.repo.uni-hannover.de/handle/123456789/3806
http://dx.doi.org/10.15488/3772
non-dipole effects
rescattering
strong-field ionization
time-dependent Schrodinger equation
Nonlinear equations
Photoionization
Schrodinger equation
Electric-dipole approximation
High-energy electron
High-order above-threshold ionization
Momentum distributions
Non-dipole effects
Rescattering
Strong field ionization
Time dependent Schrodinger equation
Momentum
High-order above-threshold ionization beyond the electric dipole approximation
oai:www.repo.uni-hannover.de:123456789/38072022-12-02T08:02:55Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
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Schreiber, Emil
author
2018
The first detections of gravitational waves have opened an exciting new field of astronomy. One of the most fundamental limitations for the sensitivity of current and future interferometric gravitational-wave detectors is imposed by the quantum nature of light: Quantum vacuum fluctuations entering the interferometer through the readout port will contribute to the detection noise, at high frequencies in the form of shot noise and at low frequencies by radiation pressure noise. A promising way to reduce this quantum noise is the injection of squeezed states of light that have a lower uncertainty in one quadrature than the vacuum state. The GEO 600 gravitational-wave detector demonstrated the use of squeezed light in 2010 and it is now the first detector to routinely apply squeezing to improve its sensitivity beyond the limits set by classical quantum shot noise. This thesis details the practical aspects of long-term stable and efficient squeezed-light integration in a large-scale gravitational-wave detector. Imperfections that can limit the amount of observable non-classical noise improvement, such as optical losses and phase fluctuations, were studied in detail and methods for their mitigation were developed. Novel control schemes for the active stabilisation of the squeezed light field's phase and alignment were one main focus of the investigations. At the same time, important experience was gathered in the operation of the squeezed light source over long timescales. Over the course of the thesis work, improvements were implemented that significantly increased the performance of the squeezed-light application. Squeezing was injected with an overall duty cycle of 88%, reaching a noise reduction of up to 4.4 dB, corresponding to a 40% lowered shot-noise level. This work has firmly established the practical application of squeezing as a mature technology. The gained knowledge will directly inform the implementation of squeezed light for all future gravitational-wave detectors.
Schreiber, Emil: Gravitational-wave detection beyond the quantum shot-noise limit : the integration of squeezed light in GEO 600. Hannover : Gottfried Wilhelm Leibniz Universität, Diss., 2018, xviii, 187 S. DOI: https://doi.org/10.15488/3773
https://www.repo.uni-hannover.de/handle/123456789/3807
http://dx.doi.org/10.15488/3773
gravitational-wave detection
squeezed light
shot noise
Gravitationswellendetektion
gequetschtes Licht
Schrotrauschen
Gravitational-wave detection beyond the quantum shot-noise limit : the integration of squeezed light in GEO 600
oai:www.repo.uni-hannover.de:123456789/39692022-12-02T08:02:55Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
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Velte, Ulrich
author
2018
Several aspects of testing the universality of free fall (UFF) with spaceborne atom interferometers are discussed. Theoretical effects that could lead to an (apparent) violation of the UFF are reviewed and the requirements for test mass material choice with respect to ultra cold atoms are discussed. Different orbit geometries for the STE-QUEST (Space Time Explorer and QUantum Equivalence principle Space Test) mission are analysed with respect to the integrated sensitivity of the UFF measurement. A reference setup of an optical phase-locked loop (OPLL) for atom interferometry is demonstrated and a theoretical model of the OPLL for phase noise assessment and optimisation is developed using Laplace transforms.
Velte, Ulrich: Orbit simulations and optical phase locking techniques for an atom interferometric test of the universality of free fall. Hannover : Gottfried Wilhelm Leibniz Universität, Diss., 2018, xi, 242 S. DOI: https://doi.org/10.15488/3935
https://www.repo.uni-hannover.de/handle/123456789/3969
http://dx.doi.org/10.15488/3935
atom interferometry
equivalence principle
satellite mission
optical phase-locked loop
gravitational physics
orbit modeling
Atominterferometrie
Äquivalenzprinzip Tests
Satellitenmission
Gravitationsphysik
Orbit simulations and optical phase locking techniques for an atom interferometric test of the universality of free fall
oai:www.repo.uni-hannover.de:123456789/42302022-12-02T15:12:31Zcom_123456789_1com_123456789_11com_123456789_15col_123456789_7col_123456789_18col_123456789_14doc-type:Articledoc-type:Textopen_accessddc:530status-type:publishedVersion
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McNeur, Joshua
author
Kozák, Martin
author
Schönenberger, Norbert
author
Leedle, Kenneth J.
author
Deng, Huiyang
author
Ceballos, Andrew
author
Hoogland, Heinar
author
Ruehl, Axel
author
Hartl, Ingmar
author
Holzwarth, Ronald
author
Solgaard, Olav
author
Harris, James S.
author
Byer, Robert L.
author
Hommelhoff, Peter
author
2018
We experimentally demonstrate several physical concepts necessary for the future development of dielectric laser accelerators—photonic elements that utilize the inelastic interaction between electrons and the optical near fields of laser-illuminated periodic nanostructures. To build a fully photonic accelerator, concatenation of elements, large energy gains, and beam steering elements are required. Staged acceleration is shown using two spatio-temporally separated interaction regions. Further, a chirped silicon grating is used to overcome the velocity dephasing of subrelativistic electrons with respect to its optical near fields, and last, a parabolic grating geometry serves for focusing of the electron beam.
McNeur, J.; Kozák, M.; Schönenberger, N.; Leedle, K.J.; Deng, H. et al.: Elements of a dielectric laser accelerator. In: Optica 5 (2018), Nr. 6, S. 687-690. DOI: https://doi.org/10.1364/OPTICA.5.000687
https://www.repo.uni-hannover.de/handle/123456789/4230
http://dx.doi.org/10.15488/4196
Inelastic interaction
Interaction region
Laser accelerators
Optical near field
Periodic nanostructure
Photonic elements
Silicon gratings
Subrelativistic electrons
Elements of a dielectric laser accelerator
oai:www.repo.uni-hannover.de:123456789/42372022-12-02T15:12:31Zcom_123456789_1com_123456789_11col_123456789_7col_123456789_14doc-type:Articledoc-type:Textopen_accessddc:530status-type:publishedVersion
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Willemsen, Thomas
author
Jupé, Marco
author
Gyamfi, Mark
author
Schlichting, Sebastian
author
Ristau, Detlev
author
2017
Dielectric components are essential for laser applications. Chirped mirrors are applied to compress the temporal pulse broadening crucial in the femtosecond regime. However, the design sensitivity and the electric field distribution of chirped mirrors is complex often resulting in low laser induced damage resistances. An approach is presented to increase the damage resistance of pulse compressing mirrors up to 190% in the NIR spectral range. Layers with critical high field intensity of a binary mirror design are substituted by ternary composites and quantized nanolaminates, respectively. The deposition process is improved by an in situ technique monitoring the phase of reflectance. © 2017 Optical Society of America.
Willemsen, T.; Jupé, M.; Gyamfi, M.; Schlichting, S.; Ristau, D.: Enhancement of the damage resistance of ultra-fast optics by novel design approaches. In: Optics Express 25 (2017), Nr. 25, S. 31948-31959. DOI: https://doi.org/10.1364/OE.25.031948
https://www.repo.uni-hannover.de/handle/123456789/4237
http://dx.doi.org/10.15488/4203
Electric fields
Laser applications
Laser damage
Mirrors
Deposition process
Design sensitivity
Dielectric components
Electric field distributions
Femtosecond regimes
In-situ techniques
Laser-induced damage resistances
Ternary composites
Laser mirrors
Enhancement of the damage resistance of ultra-fast optics by novel design approaches
oai:www.repo.uni-hannover.de:123456789/42672022-12-02T08:02:55Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
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Schwarze, Thomas S.
author
2018
This thesis was carried out in the area of gravitational physics, specifically in the fields of gravitational wave astronomy and gravimetry. Both fields do or will make use of satellite missions. The planned gravitational wave observatory Laser Interferometer Space Antenna (LISA) aims to detect gravitational waves in the mHz range while missions like the Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) and the Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) measured or will measure, respectively, the Earth’s gravity field to obtain valuable information on hydrology and climate dynamics. The first part of this thesis deals with the heterodyne interferometric readout for LISA and, in particular, its phase extraction system or phasemeter. A summary of the basic principles is followed by a statement of the requirements for the latter. These concern in particular the phase noise contribution, dynamic range and bandwidth. Subsequently, possible testing schemes are being discussed. One experimentally investigated in the scope of this thesis is an optical three-signal test which provides the ability to probe for phasemeter linearity. It utilizes an interferometer of hexagonal footprint, thus called Hexagon, to probe an elegant breadboard model of the LISA phasemeter developed prior to this thesis. An extensive noise hunt was performed to reduce testbed noise. This, in turn, allowed for a measurement in accordance with the single channel LISA requirement extrapolated to three signals (10.23µrad/ √ Hz down to 4mHz). It was conducted with heterodyne frequencies of 3–5.8MHz and a dynamic range of six orders of magnitude. A measurement with full LISA-like values for these parameters did meet the targeted performance outside the Fourier frequency range 0.4–20mHz, inside of which the utilized photoreceivers were limiting. The second thesis part describes the development and implementation of two phase readout schemes for the interferometry technique Deep Frequency Modulation Interferometry (DFMI). The latter aims to provide high scalability and dynamic range in order to interferometrically track test masses in future gravimetry missions or other applications. Two phase extraction methods were investigated, one based on a spectral analysis followed by a non-linear fit, the other on an extended Kalman filter in conjunction with empiric state space modeling. First tests included proof-of-principle tracking of moving mirrors as well as demonstrated a performance of 4µrad/ √ Hz at 0.1–1Hz.
Diese Arbeit wurde im Bereich Gravitationsphysik, oder genauer, in den Bereichen Gravitationswellenastronomie und Gravimetrie durchgeführt. Beide Bereiche nutzen oder werden in Zukunft Satellitenmissionen nutzen. Der geplante Gravitationswellendetektor Laser Interferometer Space Antenna (LISA) ist darauf ausgerichtet, Gravitationswellen im mHz Bereich zu messen, während Missionen wie Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) und Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) das Gravitationsfeld der Erde vermessen haben bzw. vermessen werden, um wertvolle Informationen für Hydrologie und Klimaforschung zu gewinnen. Der erste Teil dieser Arbeit behandelt die interferometrische Auslese in LISA und speziell die zugehörige Phasenextrahierung beziehungsweise das zugehörige Phasenmeter. Nach einer Zusammenfassung der Hauptprinzipien werden die Anforderung an Letzteres vorgestellt. Diese betreffen in erster Linie den Beitrag von Phasenrauschen, den dynamischen Bereich sowie die Bandbreite. Anschließend werden mögliche Testschemata diskutiert. Eines dieser Schemata, ein optischer Dreisignaltest, wurde in dieser Arbeit durchgeführt. Es ermöglicht die Überprüfung der Linearität des Phasenmeters. Ein Interferometer mit hexagonalem Grundriss, welches daher als Hexagon bezeichnet wird, dient als Hauptbaustein. In dieser Arbeit wird es genutzt, um einen Phasenmeterprototypen für LISA zu testen, welcher im Vorfeld dieser Arbeit entwickelt wurde. Eine ausführliche Suche nach Rauschquellen im Experiment wurde durchgeführt mit dem Ziel, diese zu beheben. Das wiederum ermöglichte eine Messung (10.23µrad/ √ Hz hinunter bis 4mHz), die Übereinstimmung mit der Anforderung für einen Auslesekanal in LISA zeigte, wenn diese auf die drei Kanäle des Dreisignaltests extrapoliert wird. Die Messung wurde mit Heterodynfrequenzen von 3–5.8MHz durchgeführt und zeigte einen dynamischen Bereich von sechs Größenordnungen. Eine Messung mit den erwarteten Signalparametern in LISA erfüllte die Anforderung im Messband abgesehen vom Intervall 0.4–20mHz. Hierbei erwiesen sich die genutzten Photoempfänger als limitierender Faktor. Der zweite Teil der Arbeit stellt die Entwicklung und Implementierung zweier Phasenausleseschemata für die Interferometrietechnik Deep Frequency Modulation Interferometry (DFMI) vor. Diese zielt auf eine hohe Skalierbarkeit und einen hohen dynamischen Bereich bei der interferometrischen Vermessung von Testmassenbewegungen ab. Dieses Verfahren kann für zukünftige Gravimetriemissionen oder in anderen Anwendungen genutzt werden. Zwei Auslesemethoden wurden untersucht. Die Erste baut auf einer Spektralanalyse mit nachfolgendem nichtlinearen Fit auf, während die zweite ein Extended Kalman Filter mit empirischer Zustandsraummodelierung darstellt. Erste Tests lieferten einen Funktionsnachweis in Form der Vermessung der Bewegung eines Spiegels. Des Weiteren wurde eine Genauigkeit von 4µrad/ √ Hz zwischen 0.1–1Hz festgestellt.
Schwarze, Thomas S.: Phase extraction for laser interferometry in space : phase readout schemes and optical testing. Hannover : Gottfried Wilhelm Leibniz Universität, Diss., 2018, xix, 196 S. DOI: https://doi.org/10.15488/4233
https://www.repo.uni-hannover.de/handle/123456789/4267
http://dx.doi.org/10.15488/4233
gravitational physics
interferometry
phase extraction
Gravitationsphysik
Interferometrie
Phasenauslese
Phase extraction for laser interferometry in space : phase readout schemes and optical testing
oai:www.repo.uni-hannover.de:123456789/43382022-12-02T08:02:55Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
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Rühmann, Steffen
author
2018
Frequenzen sind die am präzisesten messbaren physikalischen Größen. Viele Messprinzipien und Geräte basieren daher primär auf der Bestimmung der Phase und Frequenz eines genauen und stabilen Oszillators. Die präzise Bestimmung der Zeitintervalle verbessert sich mit der Erhöhung der Frequenz des periodischen Signals des Frequenzstandards. Optische Frequenzen sind gegenüber den MikrowellenAtomuhren, die aktuell noch die SI-Sekunde defnieren, um etwa vier bis fünf Größenordnungen höher und können potentiell um diesen Faktor genauer sein. Die Entwicklung des optischen Frequenzkammgenerators im Jahr 1998 von der Gruppe um Theodor W. Hänsch [1, 2], welche 2005 mit dem Physik-Nobelpreis gewürdigt wurde, hat dabei den Fortschritt der Atomuhren im optischen Bereich stark beschleunigt. Die derzeit präzisesten optischen Atomuhren erreichen inzwischen Instabilitäten und Ungenauigkeiten in der Größenordnung von 10^{−18} [3], was einem Gangunterschied von weniger als einer Sekunde in einem Zeitraum entsprechend dem Alter des Universums entspricht. Um die bestmögliche Präzision bereits in kurzen Zeitskalen zu erreichen wird ein hochstabiler Lokaloszillator benötigt, welcher die atomare Referenzfrequenz anregen und mit einer entsprechenden Stabilität zwischen den jeweiligen Messzyklen halten kann. Inzwischen liegt die erreichbare Genauigkeit atomarer Referenzen deutlich über der Stabilität der Oszillatoren. Eine Verbesserung der Stabilität von Lokaloszillatoren ist daher ein wichtiger Forschungsschwerpunkt innerhalb des Bereichs der optischen Atomuhren [4]. In dieser Arbeit zeige ich die Methode einer Stabilisierung eines Lokaloszillators, wie er für die Abfrage des in Entwicklung befndlichen Frequenzstandards basierend auf atomaren neutralem Magnesium-24 eingesetzt wird, bis zum Limit des berechneten thermischen Rauschens. Es werden Instabilitäten von 4 · 10^{−16} in 1 Sekunde erreicht mit Spitzenwerten von 2 · 10^{−16} für längere Mittelungszeiten, was unter dem berechneten thermischen Rauschen liegt, allerdings im Rahmen der statistischen Unsicherheit. Ebenso konnte die Langzeitstabilität verbessert werden. Auf eine einheitliche Resonatorlänge skaliert erreicht dieses Laserystem im weltweiten Vergleich hypothetisch nach publizierten Resultaten meines Wissens nach unter den bei Raumtemperatur stabilisierten Lasersystemen sogar die geringste Instabilität im Zeitbereich von 4 - 40 Sekunden. Die aktuell beste Instabilität (etwa einer Größenordnung besser) wird allerdings von einem Lasersystem erreicht, welches auf einen bei kryogenen Temperaturen stabilisierten Siliziumresonator referenziert ist [5]. Ein weiterer Forschungsschwerpunkt in meiner Arbeit ist die theoretische Evaluierung eines Laser-Synergie-Konzeptes und der Einfluss auf die Instabilität für eine Kurzzeitreferenz: Ich erläutere ein Konzept, wie Lasersysteme, die abseits des Forschungsbereichs von Atomuhren entwickelt wurden, ebenfalls zur Verbesserung eines Frequenzstandards genutzt werden könnten. In meinen Berechnungen zeige ich die potentiell erreichbaren Instabilitäten, die deutlich unter denen aktueller Uhrenlasersysteme liegen. Ebenso habe ich im Rahmen dieser Arbeit den aktuellen Faserlinkaufbau zwischen der PTB und dem IQ charakterisiert. So konnte ich bereits erste Laservergleiche realisieren und frühere Limitierungen für einen Frequenzvergleich der Mg-Gitteruhr, der inzwischen durchgeführt wurde, ausgeschlossen werden.
Frequencies are the physical values which can be measured most precisely. Many measurement principles and devices are therefore based on the determinination of the phase and frequency of an accurate and stable oscillator. The precise determination of time intervals improves with increasing frequency of the periodic signal explicited as frequency standard.Optical frequencies are about four to fve orders of magnitudes larger compared to current microwave frequency standards, which still defne the SI-second, and have therefore a larger potential. The development of the frequency comb in the year 1998 increased the advance in optical clock technologies. Due to their importance in frequency measurements its development was awarded with the Nobel Prize in 2005. An atomic reference defnes the accuracy of such a frequency. For that purpose it needs to be well isolated from environmental disturbances. Current most precise optical clocks achieve instabilities and accuracies in the order of 10^{−18} [3]. This would correspond to an accuracy of one second compared to the age of the universe. To achieve such a precision in short time scales an ultrastable local oscillator is necessary, which is capable of adressing the ultranarrow atomic transition and stays that stable in between the measurement cycle time. The achievable accuracy of these atomic references exceed the instabilites of the oscillators and therefore those became a limiting factor. So currently the improvement in the stability of these local oscillators is an important feld of research [4]. In this work I show how to stabilize a laser to its fundamental limit, which is the brownian thermal noise and therefore to push the limits for future setups. Instabilities in the order of 4 · 10^{−16} in 1 second are achieved with best values of 2 · 10^{−16} for integration times of a few ten seconds, which is even below the calculated thermal noise floor, but still as part of the statistical error. Additionally the long term performance could be improved. Compared to other room temperature based systems scaled to the same resonator length it achieves the lowest instability in the time scale of 4 - 40 seconds. The best published instability of a lasersystem is the cryogenic silicon resonator based lasersystem which is almost one order of magnitude better [5]. Another part of this work is the theoretical evaluation of a laser-synergy-concept to improve the short term stability of clock laser systems. I explain this concept taking laser systems into account, which originally were not ment for use in atomic clock systems. Specifcally I looked into the potential of gravitational wave detector systems. I show calculations, which indicate an improvement of clock laser systems. Additionally in this work I completed the current implementation of the fiber link between PTB and IQ and characterized its performance. I realized first laser comparisons and I could exclude former limits for frequency measurements, which where already succesful in the meantime.
Rühmann, Steffen: Frequenzstabilisierung eines hochstabilen Lasersystems bis zum Thermischen-Rausch-Limit und Berechnungen eines Laser-Synergie-Konzeptes. Hannover : Gottfried Wilhelm Leibniz Universität, Diss., 2018, viii, 112, xxxviii S. DOI: https://doi.org/10.15488/4304
https://www.repo.uni-hannover.de/handle/123456789/4338
http://dx.doi.org/10.15488/4304
Optical resonators
laser stabilization
frequency standards
Optische Resonatoren
Laserstabilisierung
Frequenzstandards
Frequenzstabilisierung eines hochstabilen Lasersystems bis zum Thermischen-Rausch-Limit und Berechnungen eines Laser-Synergie-Konzeptes
oai:www.repo.uni-hannover.de:123456789/43532022-12-02T07:47:02Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
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Ruhmann, Marc
author
2019
This thesis comprises a numerical study of high-order harmonic generation (HHG) in the hydrogen molecule H2 and its heavier isotope D2. HHG refers to the emission of high-frequency radiation by an atom or molecule when it is subject to a strong laser field. It can be explained as a series of three steps: ionization, continuum travel of the freed electron and recombination of the electron with the parent ion, releasing its acquired energy as a high-energy photon. Our central focus lies on how the harmonic signal strength differs between the isotopologues, quantified by the ratio of the emitted harmonic intensities (harmonic ratio). The molecular analogue of the Lewenstein model predicts a dependence of the dipole moment, and consequently the harmonic intensity, on the vibrational autocorrelation function. This function measures the overlap of the vibrational ground state of the neutral molecule and the time-dependent state evolving on the Born-Oppenheimer potential energy curve of the ion while the electron is in the continuum. The duration of the time evolution is determined by the time of ionization and recombination of the participating electron. The heavier nuclear mass of D2 leads to a slower vibration than in H2, which affects the time dependence of the autocorrelation and ultimately the intensity of the harmonic radiation. The analytical expression of the HHG dipole moment is typically simplified with the help of the saddle-point approximation, which leads to the peculiar result of complex-valued electron ionization and recombination times. We study the autocorrelation and in particular the ratio of autocorrelations of D2/H2 in the context of these complex times. We do so separately for the short and long trajectories, which are two distinct kinds of trajectories the electron follows during its continuum journey. The study consists of two parts. The first is purely theoretical where we compare autocorrelation ratios with harmonic ratios acquired by numerical solution of the time-dependent Schrödinger equation. The second consists of a comparison of the theoretical results with harmonic ratios determined by experiment. The theoretical comparison in the first part is done for two orientations of the molecular axis relative to the linearly polarized electric field of the driving laser pulse, parallel and perpendicular. Moreover, we employ two models of the autocorrelation function in the comparison. One uses real-valued times originating from the semiclassical three-step model and an LCAO-approximated dipole-transition matrix element. The other makes use of the complex-valued saddle-point times and an exact transition matrix element, calculated numerically via exact scattering states of the model potentials. The comparison with the experiment involves the study of the Stark effect as well as molecular alignment distributions. Additionally, also the PACER method (Probing Attosecond dynamics by Chirp-Encoded Recollision) is employed. That is, the molecular vibrational motion is reconstructed from the experimental observables on an attosecond time scale. Finally, the comparison between theory and experiment is carried out for the ammonia molecule NH3 and its heavier counterpart ND3 as well.
Diese Arbeit umfasst eine numerische Studie der Erzeugung hoher Harmonischer (HHG) im Wasserstoffmolekül H2 und dem schwereren Isotop D2. HHG bezeichnet die Emission von hochfrequenter Strahlung durch ein Atom oder Molekül welches einem starken Laserfeld ausgesetzt ist. Es kann als ein dreistufiger Prozess verstanden werden: Ionisation, Bewegung des befreiten Elektrons im Kontinuum und Rekombination des Elektrons mit dem entstandenen Ion, wobei die erlangte Energie des Elektrons in Form eines hochenergetischen Photons freigesetzt wird. Das Ziel ist die Untersuchung der unterschiedlich starken harmonischen Signale der beiden Isotope, was durch das Verhältnis der Intensitäten der Harmonischen ausgedrückt werden kann (harmonisches Verhältnis). Das molekulare Analog des Lewenstein-Modells sagt eine Abhängigkeit des Dipolmoments, und somit der Intensität der Harmonischen, von der Vibrations-Autokorrelationsfunktion voraus. Diese Funktion misst den Überlapp zwischen dem Vibrationsgrundzustand des neutralen Moleküls und dem zeitabhängigen Zustand entwickelt auf der Born-Oppenheimer Potentialkurve des Ions während das Elektron im Kontinuum ist. Die Dauer der Zeitentwicklung ist durch die Ionisations- und Rekombinationszeit des teilnehmenden Elektrons bestimmt. Die schwerere Kernmasse von D2 führt zu einer langsameren Vibration als in H2, was die Zeitentwicklung der Autokorrelation und letztendlich die Intensität der harmonischen Strahlung beeinflusst. Der analytische Ausdruck des HHG-Dipolmoments wird üblicherweise durch die Sattelpunktsnäherung vereinfacht, welches komplexwertige Ionisations- und Rekombinationszeiten des Elektrons zur Folge hat. Wir untersuchen die Autokorrelation und insbesondere das Verhältnis der Autokorrelationen von D2 und H2 hinsichtlich dieser komplexen Zeiten. Wir unterscheiden dabei explizit zwischen den kurzen und langen Trajektorien, welches zwei unterschiedliche Typen von Trajektorien sind, denen das Elektron im Kontinuum folgt. Unsere Studie besteht aus zwei Teilen. Der erste Teil ist eine rein theoretische Betrachtung, bei der wir Autokorrelationsverhältnisse mit harmonischen Verhältnissen aus numerischen Lösungen der zeitabhängigen Schrödingergleichung vergleichen. Der zweite Teil ist ein Vergleich der theoretischen Ergebnisse mit experimentellen harmonischen Verhältnissen. Der theoretische Vergleich im ersten Teil wird für zwei Orientierungen der Molekülachse zu dem linear polarisierten elektrischen Feld des Lasers durchgeführt, parallel und senkrecht. Darüber hinaus betrachten wir in dem Vergleich zwei Modelle der Autokorrelationsfunktion. Eines verwendet die reellwertigen Zeiten aus dem semiklassischen Drei-Stufen-Modell und ein Dipolübergangselement in LCAO-Näherung. Das andere benutzt die komplexwertigen Sattelpunktszeiten und ein exaktes Übergangselement, welches numerisch exakte Streulösungen der Modellpotentiale verwendet. Der Vergleich mit dem Experiment beinhaltet eine Studie des Stark-Effekts und molekularer Ausrichtungsverteilungen. Zusätzlich kommt auch die PACER-Methode zum Einsatz. Dies bedeutet, dass die Vibrationsbewegung des Molekülions aus den experimentellen Observablen auf der Attosekundenskala rekonstruiert wird. Der Vergleich zwischen Theorie und Experiment wird auch für das Ammoniakmolekül NH3 und dem schwereren Gegenstück ND3 durchgeführt.
Ruhmann, Marc: Study of the isotope-dependence of molecular high-harmonic generation in D2 and H2. Hannover : Gottfried Wilhelm Leibniz Universität, Diss., 2018, 189 S. DOI: https://doi.org/10.15488/4319
https://www.repo.uni-hannover.de/handle/123456789/4353
http://dx.doi.org/10.15488/4319
High-harmonic generation
Vibrational autocorrelation
Time-dependent Schrödinger equation
Erzeugung hoher Harmonischer
Vibrations-Autokorrelation
Zeitabhängige Schrödingergleichung
Study of the isotope-dependence of molecular high-harmonic generation in D2 and H2
oai:www.repo.uni-hannover.de:123456789/45902022-12-02T08:02:55Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
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Zipfel, Klaus Hendrik
author
2019
Mit ihren relativen Instabilitäten und Ungenauigkeiten von nur noch wenigen 10^-18 übertreffen optische Frequenzstandards bereits heutzutage die derzeit besten Mikrowellen-Atomuhren um mehrere Größenordnungen. Neben der präzisen Zeitmessung gerät auf diesem Niveau die Beantwortung fundamentaler physikalische Fragestellungen sowie die relativistische Geodäsie in greifbare Nähe. Im Falle optischer Gitteruhren wird ein Ensemble lasergekühlter neutraler Atome in einem optischen Gitter spektroskopiert. Damit das Gitterlicht die Genauigkeit der Abfrage nicht limitiert, ist dazu der Betrieb bei der magischen Wellenlänge notwendig. Hier ist die Polarisierbarkeit beider Uhrenzustände in erster Ordnung identisch, sodass die über den AC-Stark-Effekt induzierte differentielle Energieverschiebung verschwindet. In dieser Arbeit wurde erstmalig eine Gitteruhr basierend auf bosonischem Magnesium-24 realisiert. Im Vergleich zu den besten gitterbasierten Frequenzstandards mit Strontium und Ytterbium, ist Magnesium um etwa eine Größenordnung weniger sensitiv auf Schwarzkörperstrahlung. Diese über die Umgebungstemperatur verursachte Systematik stellt bei Raumtemperatur den größten frequenzverschiebenden Beitrag bei Strontium sowie Ytterbium dar und begrenzte lange Zeit auch deren Unsicherheit. Einer der Kernpunkte dieser Arbeit behandelt die Untersuchung und Minimierung von frequenzverbreiternden Mechanismen bei der Spektroskopie. Zu Beginn betrug die auflösbare Übergangslinienbreite, bedingt durch Tunneln im Gitter, mehrere kHz. Dies konnte durch ein verbessertes Gitterlasersystem gelöst werden, mit dem nun Gittertiefen von mehr als 42 ER realisierbar sind. In diesem Regime beträgt der alleinige Einfluss durch Tunnelverbreiterung nur noch bei 24 Hz, sodass weitere Verbreiterungsmechanismen in den Vordergrund treten – allem voran die Anregungsfelder sowie die Zustandspräparation im Gitter. Konsequenterweise wurden der Uhrenlaser, das benötigte Magnetfeld und die Gitterbesetzung untersucht und deren Homogenität bestmöglich sichergestellt. Anhand dieser Verbesserungen ist eine minimale Linienbreite von 51(3) Hz demonstriert worden, womit sich der beste für Magnesium realisierte Gütefaktor zu Q = 1,3×10^13 bestimmt. Der zweite Teil dieser Arbeit beschäftigt sich mit der atomaren Anbindung des Uhrenlasers sowie der Stabilitätsuntersuchung. In einem Selbstvergleich konnten so Instabilitäten von nur noch 5,1 +2,9/-1,1×10^-16 demonstriert werden. Das Integrationsverhalten war dabei vollständig durch Detektionsrauschen limitiert und lag mit 1,1×10^-14 (t/s)^(-1/2) noch deutlich über dem Dick-Limit von 1×10^-15 (t/s)^(-1/2). Aufgrund der starken Gleichtaktunterdrückung im Selbstvergleich, kann die Instabilität der Magnesium-Gitteruhr allerdings nicht unverfälscht bestimmt werden. Daher sind Stabilitätsanalysen gegen unabhängige Frequenzstandards der Physikalisch-Technischen Bundesanstalt in Braunschweig durchgeführt worden. Dazu kam ein 73 km langer Faserlink zum Einsatz, welcher der Leibniz Universität Hannover den für Universitäten einzigartigen Zugang zu einem wachsenden europäischen Frequenznetzwerk gewährt. Im Vergleich gegen eine Strontium-Gitteruhr wurde beobachtet, dass die Instabilität von Magnesium bei etwa 2×10^-15 begrenzt ist. Als Ursache sind Schwankungen in der Uhrenlaserleistung und damit einhergehende AC-Stark-Variationen identifiziert worden. Über die in situ Bestimmung dieser Abweichungen mit anschließender Nachkorrektur, konnte die Instabilität in einer zweiten Messung gegen eine Ytterbium-Ionenuhr auf 7,7 +5,0/-1,3×10^-16 reduziert werden. Dies stellt die geringste jemals mit Magnesium demonstrierte Instabilität in einer Frequenzmessung dar.
Optical frequency standards, reaching instabilities and uncertainties in the low 10^-18 regime, already surpassed their microwave counterparts by many orders of magnitude. Besides the precise measurement of time, such accurate clocks might answer fundamental physical questions or can even be used in relativistic geodesy. In the case of optical lattice clocks, a laser-cooled atomic ensemble of neutral atoms is probed while being trapped in an optical lattice. In order to not disturb the atomic transition frequency, the lattice has to be operated at the magic wavelength. Here, the polarizability of both clock states is identical in first order, such that the differential energy shift induced by the AC-Stark-effect vanishes. In the scope of this thesis, an optical lattice clock based on bosonic magnesium-24 has been realized for the first time. Compared to state-of-the-art lattice based frequency standards with strontium or ytterbium, magnesium offers an almost one order of magnitude lower sensitivity to black body radiation. This systematic shift, induced by the temperature of the environment, has the biggest contribution to the error budget for strontium and ytterbium at room temperature and limited their uncertainty for a long time. One key aspect of this thesis describes the investigation and reduction of broadening mechanisms during spectroscopy. At the beginning of this thesis, the resolved linewidth was broadened to several kHz, caused by tunneling in the lattice. An improved lattice laser system allowed reaching lattice depths of up to 42 ER. In this regime, tunneling induced broadening contributes only via 24 Hz, which made other broadening effects to become dominant such as the spectroscopy fields or the state preparation within the lattice. Therefore investigations of the clock laser, the involved magnetic field and the lattice state occupation has been performed and subsequently homogenized. With these improvements a linewidth of only 51(3) Hz has been observed, which gives rise to the best line quality factor demonstrated for magnesium of Q = 1.3×10^13. The second part of this thesis covers the lock of the clock laser to the atomic transition and the investigation of the overall stability. By utilizing a self-comparison, an instability of 5.1 +2.9/-1.1×10^-16 has been demonstrated. The integration behavior of 1.1×10-14(t/s)^(-1/2) was completely limited by detection noise, which was significantly bigger than the Dicklimit of 1×10-15(t/s)^(-1/2). The real instability of the magnesium frequency standard cannot be deduced via a self-comparison due to the high common mode suppression. Therefore an instability analysis against independent optical frequency standards at the Physikalisch-Technische Bundesanstalt in Brunswick has been performed. For this a 73 km long fiber link has been used which allows the Leibniz Universität Hannover the exceptional access to a growing European frequency network. By comparing against a strontium lattice clock, an instability limit of 2×10^-15 for the magnesium frequency standard has been observed. Intensity fluctuations of the clock laser and thus varying AC-Stark shifts have been identified to cause this limitation. By measuring these time dependent shifts in situ, the total instability in a comparison against an ytterbium ion clock could be reduced to 7.7 +5.0/-1.3×10^-16 via a post correction. This represents the lowest instability of a magnesium frequency standard in an independent frequency comparison so far.
Zipfel, Klaus Hendrik: Hochauflösende Spektroskopie und Stabilitätsanalyse eines Magnesium-Frequenzstandards. Hannover : Gottfried Wilhelm Leibniz Universität, Diss., 2019, iv, 136 S. DOI: https://doi.org/10.15488/4548
https://www.repo.uni-hannover.de/handle/123456789/4590
http://dx.doi.org/10.15488/4548
Magnesium lattice clock
resolution
stability
frequency comparison
fiber link
Magnesium Gitteruhr
Auflösung
Stabilität
Frequenzvergleich
Faserlink
Hochauflösende Spektroskopie und Stabilitätsanalyse eines Magnesium-Frequenzstandards
oai:www.repo.uni-hannover.de:123456789/47442022-12-02T08:02:55Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
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Rudolph, Jan
author
2016
Quantum sensors based on the interference of cold atoms have advanced to the forefront of precision measurements in geodesy, metrology and tests of fundamental physics. The ultimate potential of these devices is realized using quantum degenerate atoms in extended free fall. This can be achieved on microgravity platforms such as drop towers, parabolic flights, ballistic rockets, satellites and space stations. The transition to mobile and robust devices that can withstand the demands of these environments comes with many challenges. Quantum sensors need to be scaled down and integrated without compromising their performance. In fact, they need to significantly outpace conventional instruments, since microgravity time is an expensive resource and limited to a few seconds at a time on the most accessible platforms.
This thesis describes the construction, qualification and operation of a miniaturized ultracold atom experiment that meets these challenges. The QUANTUS-2 apparatus features a payload weight of 147 kg and a payload volume of 0.3 m^3. It generates Bose-Einstein condensates of 4×10^5 ^87Rb atoms every 1.6 seconds, a flux of ultra-cold atoms that is on par with the best lab-sized devices. Ensembles of 1×10^5 atoms can be created at a 1 Hz rate. It is currently the fastest machine of its kind and achieves the highest atom number of any atom chip setup. The apparatus continuously withstands peak accelerations of up to 45 g during microgravity campaigns at the drop tower facility in Bremen, Germany. Here, the payload has accrued 208 drops and 9 catapult launches over 24 month. The setup is the first atom optics experiment to stand up to the technical demands of catapult operation. Four condensates can be created and observed consecutively during nine seconds of free fall in a single catapult launch. In total, the experiment has been suspended in microgravity for over 17 minutes. With the record source performance, the repetition rate for microgravity experiments with ultra-cold atoms was increased by a factor of four compared to previous devices. The total atom number was increased by a factor of 40, vastly improving the signal to noise ratio for absorption images of spatially extended clouds. The ensembles can be prepared consistently over many weeks of drop tower operation. The variance of the mean center of mass velocity in two observable directions is 7.3 μm/s and 6.9 μm/s. Magnetic lensing techniques were employed to manipulate the expansion of the ensembles. First results yield a residual expansion rate in three dimensions of σ_v = 116.9 ± 13.9 μm/s, which implies a three-dimensional effective temperature of T = 47.6 ± 11.3 pK at an average condensate atom number of N = 93000. These values constitute the best collimation of any atomic ensemble and the most promising source for atom interferometry reported to date. Optimizing the current lensing sequence will reduce the expansion rate further to effective temperatures in the femtokelvin regime. The level of control demonstrated over the condensates is highly relevant for the advancement of matter-wave optics and quantum sensors. Controlling the motion and size of atomic clouds is intrinsically tied to many systematic effects in high precision measurements. QUANTUS-2 will provide a platform to explore and mitigate these limitations on unprecedented time scales of up to seven seconds of free evolution.
Rudolph, Jan: Matter-wave optics with Bose-Einstein condensates in microgravity. Hannover : Gottfried Wilhelm Leibniz Universität, Diss., 2016, 198 S. http://nbn-resolving.de/urn:nbn:de:gbv:089-8716157700
https://www.repo.uni-hannover.de/handle/123456789/4744
http://dx.doi.org/10.15488/4702
Bose-Einstein condensates
Matter-waves
Microgravity
Bose-Einstein Kondensate
Matteriewellen
Mikrogravitation
Matter-wave optics with Bose-Einstein condensates in microgravity
oai:www.repo.uni-hannover.de:123456789/51992022-12-02T08:02:55Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
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Corgier, Robin
author
2019
Modern physics relies on two distinct fun- damental theories, General Relativity and Quantum Mechanics. Both describe on one hand macroscopic and cosmological phenomena such as gravitational waves and black holes and on the other hand micro- scopic phenomena as superfluidity or the spin of par- ticles. The unification of these two theories remains, so far, an unsolved problem. Interestingly, candidate Quantum Gravity theories predict a violation of the principles of General Relativity at different levels. It is, therefore, of a timely interest to detect violations of these principles and determine at which level they occur.
Corgier, Robin: Engineered atomic states for precision interferometry. Hannover : Gottfried Wilhelm Leibniz Universität, Diss., 2019, xvi, 192 S. DOI: https://doi.org/10.15488/5152
https://www.repo.uni-hannover.de/handle/123456789/5199
http://dx.doi.org/10.15488/5152
Shortcut-to-adiabaticity (STA)
optimal control theory (OCT)
thermal ensemble
Bose-Einstein condensates (BEC)
BEC mixtures
atom chip
Abkürzung zur Adiabatizität
Theorie der optimalen Steuerungen (TOS)
thermisches Ensemble
Bose-Einstein-Kondensate (BEK)
BEC-Mischungen
Atomchips
Engineered atomic states for precision interferometry
oai:www.repo.uni-hannover.de:123456789/52072022-12-02T07:47:03Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
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Burgermeister, Tobias
author
2019
Single ion frequency standards have demonstrated in several experiments excellent results and are approaching fractional frequency uncertainties of 10^-18. As dominant contributions to the uncertainty are linked to the ion trap properties a further reduction would be possible by an improved ion trap. Due to the interrogation of a single ion these frequency standards are currently limited by the intrinsically low signal-to-noise ratio and require long averaging times on the order of several days. This limitation is critical for various applications that require a high frequency resolution on short timescales. One possibility to improve the clock stability is to increase the number of clock ions. However, this approach further increases the requirements for the ion trap. Therefore, for the realization of a multi-ion clock that aims at simultaneously reducing
the frequency stability and uncertainty the control over the characteristics of the ion
trap is crucial.
This thesis continues previous work towards the realization of a multi-ion optical clock based on ion Coulomb crystals of 115In+ ions which are sympathetically cooled by 172Yb+ ions. The existing design for a segmented linear ion trap has been refined and a reliable trap manufacturing process for a trap based on gold coated aluminium nitride wafers has been developed. Manufacturing tolerances below 10 μm allowed to reduce the axial micromotion amplitudes substantially. For a region of more than 300 μm the uncertainty contribution of the three-dimensional micromotion amplitude is shown to be below 10^-19. Additionally the radial ion heating rate of the trap has been measured to be 1.1 phonons/s for a trap frequency of 490 kHz. The time dilation shift due to the heating rate on the radial trap axis is found to be (2.1 ± 0.3) x 10^-20 1/s.
The trap design has also been optimized for a low trap temperature rise due to the applied rf voltage. Trap temperature measurements with Pt100 sensors installed on the trap showed a maximum temperature increase of 1.21 K at an rf voltage amplitude of 1 kV. By comparing the measurement results to FEM simulations the uncertainty contribution of the trap temperature to the black-body radiation shift has been deduced to be 2.4 x 10^-20.
As the ion trap provides a high level of control on Coulomb crystals it also provides an ideal test bed for studying atomic many-body systems. This work presents results of the investigations on topological defects in two-dimensional Coulomb crystals. The emphasis was placed on the effects of mass defects and external electric fields on the stability of the topological defects. It is shown that these effects can be used to
manipulate and create topological defects deterministically.
In mehreren Experimenten haben Frequenzstandards auf der Basis von einzelnen Ionen hervorragende Ergebnisse erzielt und nähern sich einer relativen Frequenzunsicherheit von 10^-18 an. Eine weitere Reduzierung der Frequenzunsicherheit wäre durch eine verbesserte Ionenfalle möglich, da dominante Beiträge der Frequenzunsicherheit auf die Eigenschaften der Ionenfalle zurückzuführen sind. Aufgrund der Abfrage eines einzelnen Ions sind diese Frequenznormale zur Zeit durch das intrinsisch niedrige Signal-Rausch-Verhältnis limitiert und benötigen lange Mittelungszeiten in der Größenordnung von mehreren Tagen. Diese Limitierung ist für verschiedene Anwendungen, die eine hohe Frequenzauflösung nach kurzen Mittelungszeiten erfordern, ein kritischer Punkt. Die Frequenzstabilität kann durch eine höhere Anzahl von Uhrenionen verbessert werden. Allerdings werden durch diesen Ansatz auch die Anforderungen an die Ionenfalle weiter erhöht. Aus diesem Grund ist für die Realisierung einer Multi-Ionen Uhr, die gleichzeitig
die Frequenzstabilität und -unsicherheit weiter verringern soll, die Kontrolle über die Eigenschaften der Ionenfalle von entscheidender Bedeutung.
Diese Dissertation setzt frühere Arbeiten zur Realisierung einer optischen Multi-Ionen-Uhr auf der Basis von Coulomb-Kristallen aus 115In+-Ionen, die durch 172Yb+-Ionen sympathisch gekühlt werden, fort. Das existierende Design einer segmentierten linearen Ionenfalle wurde optimiert und es wurde ein zuverlässiger Herstellungsprozess basierend auf goldbeschichteten Aluminiumnitrid-Wafern entwickelt. Durch Fertigungstoleranzen von weniger als 10 μm konnte die axiale Mikrobewegungsamplitude deutlich reduziert werden. Es wird gezeigt, dass in einem Bereich von über 300 μm der Beitrag der dreidimensionalen Mikrobewegung zur Frequenzunsicherheit unterhalb von 10^-19 ist. Zusätzlich wurde die radiale Heizrate der Falle mit 1,1 Phononen/s bei einer Fallenfrequenz von 490 kHz bestimmt. Die Frequenzverschiebung durch Zeitdilatation durch die Heizrate der radialen Fallenachse beträgt damit (2,1 ± 0,3) x 10^-20 1/s.
Das Fallendesign wurde ebenso auf einen geringen Anstieg der Fallentemperatur durch die angelegte HF-Spannung optimiert. Die Messungen der Fallentemperatur mit den auf der Falle installierten Pt100 Sensoren zeigten einen maximalen Temperaturanstieg von 1,21 K bei einer HF-Spannungsamplitude von 1 kV. Durch den Vergleich der Messergebnisse mit FEM-Simulationen wurde der Beitrag der Fallentemperatur zur Frequenzverschiebung durch die Schwarzkörperstrahlung mit 2,4 x 10^-20 bestimmt.
Da die Ionenfalle eine sehr gute Kontrolle über Coulomb-Kristalle bietet, eignet sie sich auch hervorragend für Experimente mit atomaren Vielteilchensystemen. Hierzu werden in dieser Arbeit Untersuchungen topologischer Defekte in zweidimensionalen Coulomb-Kristallen vorgestellt. Der Schwerpunkt lag dabei auf der Analyse des Einflusses von Massendefekten und externen elektrischen Feldern auf die Stabilität der topologischen Defekte. Es wird gezeigt wie dieser Einfluss genutzt werden kann, um die Defekte gezielt zu manipulieren und sie deterministisch zu produzieren.
Burgermeister, Tobias: Development and characterization of a linear ion trap for an improved optical clock performance. Hannover : Gottfried Wilhelm Leibniz Universität, Diss., 2019, xiii, 144 S. DOI: https://doi.org/10.15488/5160
https://www.repo.uni-hannover.de/handle/123456789/5207
http://dx.doi.org/10.15488/5160
ion traps
optical clocks
excess micromotion
Coulomb crystals
many-body systems
Ionenfallen
optische Uhren
Mikrobewegung
Coulomb-Kristalle
Vielteilchensysteme
Development and characterization of a linear ion trap for an improved optical clock performance
oai:www.repo.uni-hannover.de:123456789/54112022-12-02T19:35:27Zcom_123456789_11col_123456789_14doc-type:Textdoc-type:ConferenceObjectopen_accessddc:530status-type:publishedVersion
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2019
This document contains the program and the abstracts of the conference "Quantum Metrology and Physics beyond the Standard Model" which was held from Jun 12th to June 14th, 2019.
Klempt, C. (Hrsg.): Conference Program - Quantum Metrology and Physics beyond the Standard Model 2019. Hannover : Institutionelles Repositorium der Leibniz Universität Hannover, 2019, 118 S. DOI: https://doi.org/10.15488/5364
https://www.repo.uni-hannover.de/handle/123456789/5411
http://dx.doi.org/10.15488/5364
Quantum Metrology
Quantum Physics
Conference
Conference Program - Quantum Metrology and Physics beyond the Standard Model 2019
oai:www.repo.uni-hannover.de:123456789/81202022-12-02T07:32:52Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
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Großardt, André
author
2013
[no abstract]
Großardt, André: Die Schrödinger-Newton-Gleichung als Modell selbstgravitierender Quantensysteme. Hannover : Gottfried Wilhelm Leibniz Universität Hannover, Diss, 2013, 154 S.
https://www.repo.uni-hannover.de/handle/123456789/8120
http://dx.doi.org/10.15488/8067
Schrödinger-Newton equation
quantum mechanics
Schrödinger-Newton-Gleichung
Quantenmechanik
Gravitation
Die Schrödinger-Newton-Gleichung als Modell selbstgravitierender Quantensysteme
oai:www.repo.uni-hannover.de:123456789/82662022-12-02T07:54:06Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
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Affeldt, Christoph
author
2014
[no abstract]
Affeldt, Christoph: Laser power increase for GEO 600 : commissioning aspects towards an operation of GEO 600 at high laser power. Hannover : Gottfried Wilhelm Leibniz Universität Hannover, Diss., 2014, 219 S.
https://www.repo.uni-hannover.de/handle/123456789/8266
http://dx.doi.org/10.15488/8213
Gravitational wave detector
laser power increase
stray light
Gravitationswellendetektor
Laserleistungserhöhung
Streulicht
Laser power increase for GEO 600 : commissioning aspects towards an operation of GEO 600 at high laser power
oai:www.repo.uni-hannover.de:123456789/82672022-12-02T07:54:06Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessstatus-type:publishedVersionddc:520doc-type:DoctoralThesis
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Aksteiner, Steffen
author
2014
[no abstract]
Aksteiner, Steffen: Geometry and analysis on black hole spacetimes. Hannover : Gottfried Wilhelm Leibniz Universität Hannover, Diss., 2014, 117 S.
https://www.repo.uni-hannover.de/handle/123456789/8267
http://dx.doi.org/10.15488/8214
General relativity
black holes
stability
Allgemeine Relativitätstheorie
schwarze Löcher
Stabilität
Geometry and analysis on black hole spacetimes
oai:www.repo.uni-hannover.de:123456789/82692022-12-02T07:54:06Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
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Amairi ep Pyka, Sana
author
2014
[no abstract]
Amairi ep Pyka, Sana: A long optical cavity for sub-Hertz laser spectroscopy. Hannover : Gottfried Wilhelm Leibniz Universität Hannover, Diss., 2014, 153 S.
https://www.repo.uni-hannover.de/handle/123456789/8269
http://dx.doi.org/10.15488/8216
Optical cavities
frequency stabilization
thermal noise
optical clock
vibration sensivity
Optischer Resonator
Frequenzstabilisierung
thermisches Rauschen
optische Uhr
Vibrationsempfindlichkeit
A long optical cavity for sub-Hertz laser spectroscopy
oai:www.repo.uni-hannover.de:123456789/82732022-12-02T07:54:06Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
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Audley, Heather E.
author
2014
[no abstract]
Audley, Heather E.: Preparing for LISA pathfinder operations : characterisation of the optical metrology system. Hannover : Gottfried Wilhelm Leibniz Universität Hannover, Diss., 2014, 374 S.
https://www.repo.uni-hannover.de/handle/123456789/8273
http://dx.doi.org/10.15488/8220
LISA pathfinder
gravitational waves
space interferometry
control loops
noise characterisation
Gravitationswellen
Weltrauminterferometrie
Regelschleifen
Rauschcharakterisierung
Preparing for LISA pathfinder operations : characterisation of the optical metrology system
oai:www.repo.uni-hannover.de:123456789/83352022-12-02T07:54:06Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
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Kahmann, Max Georg Günther
author
2014
[no abstract]
Kahmann, Max Georg Günther: Link between photoassociation and optical Feshbach resonances through the example of calcium. Hannover : Gottfried Wilhelm Leibniz Universität Hannover, Diss., 2014, 157 S.
https://www.repo.uni-hannover.de/handle/123456789/8335
http://dx.doi.org/10.15488/8282
Ultra-cold atoms
photoassociation spectroscopy
optical Feshbach resonances
scattering length
optical length
cold molecules
multi-photon photoassociation
Bragg spectroscopy
magnetic storage
Gallagher-Pritchard losses
calcium
Ultrakalte Atome
Photoassoziationsspektroskopie
optische Feshbachresonanzen
Streulänge
optische Länge
kalte Moleküle
Multiphotonenphotoassoziation
Braggspektroskopie
magnetisches Speichern
Gallagher-Pritchard-Verluste
Kalzium
Link between photoassociation and optical Feshbach resonances through the example of calcium
oai:www.repo.uni-hannover.de:123456789/83392022-12-02T07:54:06Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
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Kaufer, Henning
author
2014
[no abstract]
Kaufer, Henning: Opto-mechanics in a Michelson-Sagnac interferometer. Hannover : Gottfried Wilhelm Leibniz Universität Hannover, Diss., 2014, 179 S.
https://www.repo.uni-hannover.de/handle/123456789/8339
http://dx.doi.org/10.15488/8286
SiN membranes
opto-mechanics
cryogenics
SiN Membranen
Opto-mechanik
Kryogenik
Opto-mechanics in a Michelson-Sagnac interferometer
oai:www.repo.uni-hannover.de:123456789/83782022-12-02T07:54:06Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
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Matjeschk, Robert
author
2014
[no abstract]
Matjeschk, Robert: First-order corrections to the mean-field limit and quantum walks with non-orthogonal position states. Hannover : Gottfried Wilhelm Leibniz Universität Hannover, Diss., 2014, XIV, 123 S.
https://www.repo.uni-hannover.de/handle/123456789/8378
http://dx.doi.org/10.15488/8325
Mean field theory
many-particle systems
quantum physics
Meanfieldnäherung
Vielteilchensysteme
Quantenphysik
First-order corrections to the mean-field limit and quantum walks with non-orthogonal position states
oai:www.repo.uni-hannover.de:123456789/83942022-12-02T07:54:06Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:330status-type:publishedVersiondoc-type:DoctoralThesis
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Parvathi, Priyanka
author
2014
[no abstract]
Parvathi, Priyanka: Assessing the adoption and impact of organic and fair trade certification of pepper in India. Hannover : Gottfried Wilhelm Leibniz Universität Hannover, Diss., 2014, 208 S.
https://www.repo.uni-hannover.de/handle/123456789/8394
http://dx.doi.org/10.15488/8341
Adoption
fair trade
impact
organic farming
poverty
Armut
Auswirkungen
fairer Handel
ökologische Landwirtschaft
Assessing the adoption and impact of organic and fair trade certification of pepper in India
oai:www.repo.uni-hannover.de:123456789/84142022-12-02T07:54:06Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
00925njm 22002777a 4500
dc
Schlippert, Dennis
author
2014
[no abstract]
Schlippert, Dennis: Quantum tests of the universality of free fall. Hannover : Gottfried Wilhelm Leibniz Universität Hannover, Diss., 2014, II, 107 S.
https://www.repo.uni-hannover.de/handle/123456789/8414
http://dx.doi.org/10.15488/8361
Matter wave interferometry
universality of free fall
precision measurements
Materialwelleninterferometrie
Universalität des freien Falls
Präzisionsmessungen
Quantum tests of the universality of free fall
oai:www.repo.uni-hannover.de:123456789/84212022-12-02T07:54:06Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
00925njm 22002777a 4500
dc
Seidel, Stephan Tobias
author
2014
[no abstract]
Seidel, Stephan Tobias: Eine Quelle für die Interferometrie mit Bose-Einstein-Kondensaten auf Höhenforschungsraketen. Hannover : Gottfried Wilhelm Leibniz Universität Hannover, Diss., 2014, 157 S.
https://www.repo.uni-hannover.de/handle/123456789/8421
http://dx.doi.org/10.15488/8368
Bose-Einstein condensation
micro gravity research
atom interferometry
Bose-Einstein-Kondensation
Weltraumforschung
Materiewelleninterferometrie
Eine Quelle für die Interferometrie mit Bose-Einstein-Kondensaten auf Höhenforschungsraketen
oai:www.repo.uni-hannover.de:123456789/84362022-12-02T07:59:27Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
00925njm 22002777a 4500
dc
Wan, Yong
author
2014
[no abstract]
Wan, Yong: Quantum logic spectroscopy of atomic and molecular ions. Hannover : Gottfried Wilhelm Leibniz Universität Hannover, Diss., 2014, XII, 175 S.
https://www.repo.uni-hannover.de/handle/123456789/8436
http://dx.doi.org/10.15488/8383
Sideband cooling
photon recoil spectroscopy
quantum logic technique
Seitenbandkühlung
Photon-Rückstoß-Spektroskopie
Quantenlogik-Techn
Quantum logic spectroscopy of atomic and molecular ions
oai:www.repo.uni-hannover.de:123456789/84372022-12-02T07:59:27Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
00925njm 22002777a 4500
dc
Wang, Yan
author
2014
[no abstract]
Wang, Yan: On inter-satellite laser ranging, clock synchronization and gravitational wave data analysis. Hannover : Gottfried Wilhelm Leibniz Universität Hannover, Diss., 2014, 294 S.
https://www.repo.uni-hannover.de/handle/123456789/8437
http://dx.doi.org/10.15488/8384
Gravitational wave data analysis
precise laser ranging
clock synchronization
Datenanalyse von Gravitationswellen
Präzisions Laser Ranging
Uhrensynchronisation
On inter-satellite laser ranging, clock synchronization and gravitational wave data analysis
oai:www.repo.uni-hannover.de:123456789/84582022-12-02T07:54:06Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
00925njm 22002777a 4500
dc
Barke, Simon
author
2015
[no abstract]
Barke, Simon: Inter-spacecraft frequency distribution for future gravitational wave observatories. Hannover : Gottfried Wilhelm Leibniz Universität Hannover, Diss., 2015, XIX, 197 S.
https://www.repo.uni-hannover.de/handle/123456789/8458
http://dx.doi.org/10.15488/8405
Gravitational waves
laser interferometry
timing noise
Graviationswellen
Laserinterferometrie
Zeitrauschen
Inter-spacecraft frequency distribution for future gravitational wave observatories
oai:www.repo.uni-hannover.de:123456789/84892022-12-02T07:59:27Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
00925njm 22002777a 4500
dc
Duhme, Jörg
author
2015
[no abstract]
Duhme, Jörg: Quantum key security : theory and analysis of experimental realisations. Hannover : Gottfried Wilhelm Leibniz Universität Hannover, Diss., 2015, 183 S.
https://www.repo.uni-hannover.de/handle/123456789/8489
http://dx.doi.org/10.15488/8436
Continuous variable quantum cryptography
hybrid reconciliation
runtime analysis
asymmetric protocol
Quanten-Schlüsselerzeugung
hybride Fehlerkorrektur
Laufzeitanalyse
asymmetrische Protokolle
Quantum key security : theory and analysis of experimental realisations
oai:www.repo.uni-hannover.de:123456789/85092022-12-02T07:54:06Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
00925njm 22002777a 4500
dc
Gebert, Florian
author
2015
[no abstract]
Gebert, Florian: Precision measurement of the isotopic shift in calcium ions using photon recoil spectroscopy. Hannover : Gottfried Wilhelm Leibniz Universität Hannover, Diss., 2015, XIV, 107 S.
https://www.repo.uni-hannover.de/handle/123456789/8509
http://dx.doi.org/10.15488/8456
Precision spectroscopy
isotope shift
UV single mode fiber
Präzisionsspektroskopie
Isotopieverschiebung
einmodige UV Faser
Precision measurement of the isotopic shift in calcium ions using photon recoil spectroscopy
oai:www.repo.uni-hannover.de:123456789/85232022-12-02T07:59:27Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
00925njm 22002777a 4500
dc
Häfner, Sebastian
author
2015
[no abstract]
Häfner, Sebastian: Ultra-stabile Lasersysteme für Weltraum- und Bodenanwendungen. Hannover : Gottfried Wilhelm Leibniz Universität Hannover, Diss., 2015, 174 S.
https://www.repo.uni-hannover.de/handle/123456789/8523
http://dx.doi.org/10.15488/8470
Frequenzy stabilization
optical cavities
thermal noise
optical clock
Frequenzstabilisierung
optische Referenzresonatoren
thermisches Rauschen
optische Uhren
Ultra-stabile Lasersysteme für Weltraum- und Bodenanwendungen
oai:www.repo.uni-hannover.de:123456789/85412022-12-02T07:59:27Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
00925njm 22002777a 4500
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Keller, Jonas
author
2015
[no abstract]
Keller, Jonas: Spectroscopic characterization of ion motion for an optical clock based on Coulomb crystals. Hannover : Gottfried Wilhelm Leibniz Universität Hannover, Diss., 2015, VI, 129 S.
https://www.repo.uni-hannover.de/handle/123456789/8541
http://dx.doi.org/10.15488/8488
Optical clocks
Coulomb crystals
ultra-stable lasers
spectroscopy
Optische Uhren
Coulombkristalle
ultrastabile Laser
Spektoskopie
Spectroscopic characterization of ion motion for an optical clock based on Coulomb crystals
oai:www.repo.uni-hannover.de:123456789/85472022-12-02T07:59:27Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
00925njm 22002777a 4500
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Korsakova, Natalia
author
2015
[no abstract]
Korsakova, Natalia: Probing low gravity gradient with LISA pathfinder. Hannover : Gottfried Wilhelm Leibniz Universität Hannover, Diss., 2015, xiv, 219 S.
https://www.repo.uni-hannover.de/handle/123456789/8547
http://dx.doi.org/10.15488/8494
Bayessian data analysis
alternative theories of gravity
space-born gravitational wave detectors
Bayessche Datenanalyse
alternative Gravitationstheorien
weltraumgebundene Gravitationswellendetektoren
Probing low gravity gradient with LISA pathfinder
oai:www.repo.uni-hannover.de:123456789/85522022-12-02T07:59:27Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
00925njm 22002777a 4500
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Kruse, Ilka
author
2015
[no abstract]
Kruse, Ilka: Quantum metrology with Einstein-Podolsky-Rosen entangled atoms. Hannover : Gottfried Wilhelm Leibniz Universität Hannover, Diss., 2015, vi, 99 S.
https://www.repo.uni-hannover.de/handle/123456789/8552
http://dx.doi.org/10.15488/8499
Einstein-Podolsky-Rosen entanglement
quantum metrology
automatized optimization
Einstein-Podolsky-Rosen-Verschränkung
Quantenmetrologie
automatisierte Optimierung
Quantum metrology with Einstein-Podolsky-Rosen entangled atoms
oai:www.repo.uni-hannover.de:123456789/85552022-12-02T07:59:27Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
00925njm 22002777a 4500
dc
Kulosa, André Philipp
author
2015
[no abstract]
Kulosa, André Philipp: Lamb-Dicke spectroscopy of the 1S0 → 3P0 transition in 24Mg and precise determination of the magic wavelength. Hannover : Gottfried Wilhelm Leibniz Universität Hannover, Diss., 2015, iv, 136 S.
https://www.repo.uni-hannover.de/handle/123456789/8555
http://dx.doi.org/10.15488/8502
Optical atomic clocks
magic wavelength
optical spectroscopy of Bloch bands
Optische Atomuhr
magische Wellenlänge
optische Spektroskopie der Blochbänder
Lamb-Dicke spectroscopy of the 1S0 → 3P0 transition in 24Mg and precise determination of the magic wavelength
oai:www.repo.uni-hannover.de:123456789/85722022-12-02T07:59:27Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
00925njm 22002777a 4500
dc
Lörch, Niels
author
2015
[no abstract]
Lörch, Niels: Laser theory for quantum optomechanics. Hannover : Gottfried Wilhelm Leibniz Universität Hannover, Diss., 2015, XII, 119 S.
https://www.repo.uni-hannover.de/handle/123456789/8572
http://dx.doi.org/10.15488/8519
Laser theory
quantum optomechanics
trapped ions
Laser Theorie
Quanten-Optomechanik
gefangene Ionen
Laser theory for quantum optomechanics
oai:www.repo.uni-hannover.de:123456789/85792022-12-02T07:59:27Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
00925njm 22002777a 4500
dc
Mahnke, Jan
author
2015
[no abstract]
Mahnke, Jan: A continuously pumped reservoir of ultracold atoms. Hannover : Gottfried Wilhelm Leibniz Universität Hannover, Diss., 2015, vi, 97 S.
https://www.repo.uni-hannover.de/handle/123456789/8579
http://dx.doi.org/10.15488/8526
Ultracold quantum gases
continuous sources
mesoscopic atom chip
Ultrakalte Quantengase
kontinuierliche Quellen
mesoskopischer Atomchip
A continuously pumped reservoir of ultracold atoms
oai:www.repo.uni-hannover.de:123456789/85982022-12-02T07:59:27Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
00925njm 22002777a 4500
dc
Otto, Markus
author
2015
[no abstract]
Otto, Markus: Time-delay interferometry simulations for the laser interferometer space antenna. Hannover : Gottfried Wilhelm Leibniz Universität Hannover, Diss., 2016, xx, 282 S.
https://www.repo.uni-hannover.de/handle/123456789/8598
http://dx.doi.org/10.15488/8545
Gravitational waves
time-delay interferometry
LISA simulation
Gravitationswellen
LISA-Simulation
Time-delay interferometry simulations for the laser interferometer space antenna
oai:www.repo.uni-hannover.de:123456789/86012022-12-02T07:59:27Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
00925njm 22002777a 4500
dc
Peise, Jan Christopher
author
2015
[no abstract]
Peise, Jan Christopher: Non-classical states of matter in spinor Bose-Einstein condensates. Hannover : Gottfried Wilhelm Leibniz Universität Hannover, Diss., 2015, v, 45 S.
https://www.repo.uni-hannover.de/handle/123456789/8601
http://dx.doi.org/10.15488/8548
Bose-Einstein condensate
spin dynamics
entanglement
Einstein-Podolsky-Rosen correlation
quantum Zeno effect
interaction-free measurements
Bose-Einstein-Kondensat
Spindynamik
Verschränkung
Einstein-Podolsky-Rosen-Korrelationen
Quanten-Zeno-Effekt
wechselwirkungsfreie Quantenmessungen
Non-classical states of matter in spinor Bose-Einstein condensates
oai:www.repo.uni-hannover.de:123456789/86092022-12-02T07:59:27Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
00925njm 22002777a 4500
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Richter, Florian
author
2015
[no abstract]
Richter, Florian: Ultracold chemistry and its reaction kinetics. Hannover : Gottfried Wilhelm Leibniz Universität Hannover, Diss., 2015, 122 S.
https://www.repo.uni-hannover.de/handle/123456789/8609
http://dx.doi.org/10.15488/8556
Ultracold quantum gases
ultracold molecules
entanglement
Ultrakalte Quantengase
ultrakalte Moleküle
Verschränkung
Ultracold chemistry and its reaction kinetics
oai:www.repo.uni-hannover.de:123456789/86292022-12-02T07:59:27Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
00925njm 22002777a 4500
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Schütze, Daniel
author
2015
[no abstract]
Schütze, Daniel: Intersatellite laser interferometry : test environments for GRACE follow-on. Hannover : Gottfried Wilhelm Leibniz Universität Hannover, Diss., 2014, 169 S.
https://www.repo.uni-hannover.de/handle/123456789/8629
http://dx.doi.org/10.15488/8576
GRACE follow-on
intersatellite interferometry
space instrumentation
Intersatelliten-Interferometrie
Raumfahrttechnologie
Intersatellite laser interferometry : test environments for GRACE follow-on
oai:www.repo.uni-hannover.de:123456789/86462022-12-02T07:59:27Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
00925njm 22002777a 4500
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Vogt, Stefan
author
2015
[no abstract]
Vogt, Stefan: Eine transportable optische Gitteruhr basierend auf Strontium. Hannover : Gottfried Wilhelm Leibniz Universität Hannover, Diss., 2015, XI, 176 S.
https://www.repo.uni-hannover.de/handle/123456789/8646
http://dx.doi.org/10.15488/8593
Optical clocks
frequency standards
lattice clocks
transportable clocks
laser cooling
permanent magnet Zeeman slower
Optische Uhren
Frequenzstandards
Gitteruhren
transportable Uhren
Strontium
Laserkühlung
Zeeman-Abbremser aus Permanentmagneten
Eine transportable optische Gitteruhr basierend auf Strontium
oai:www.repo.uni-hannover.de:123456789/86572022-12-02T07:59:27Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
00925njm 22002777a 4500
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Wittel, Holger
author
2015
[no abstract]
Wittel, Holger: Active and passive reduction of high order modes in the gravitational wave detector GEO 600. Hannover : Gottfried Wilhelm Leibniz Universität Hannover, Diss., 2015, XII, 225 S.
https://www.repo.uni-hannover.de/handle/123456789/8657
http://dx.doi.org/10.15488/8604
GEO 600
gravitational wave detector
high order modes
thermal compensation
astigmatism
Gravitationswellendetektor
Moden höherer Ordnung
thermische Kompensation
Astigmatismus
Active and passive reduction of high order modes in the gravitational wave detector GEO 600
oai:www.repo.uni-hannover.de:123456789/86802022-12-02T07:59:27Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
00925njm 22002777a 4500
dc
Al-Masoudi, Ali Khalas Anfoos
author
2016
[no abstract]
Al-Masoudi, Ali Khalas Anfoos: A strontium lattice clock with reduced blackbody radiation shift. Hannover : Gottfried Wilhelm Leibniz Universität Hannover, Diss., 2016, ix, 132 S.
https://www.repo.uni-hannover.de/handle/123456789/8680
http://dx.doi.org/10.15488/8627
Frequency standards
blackbody radiation shift
absolute frequency
Frequenzstandards
Schwarzkörperverschiebung
Absolutfrequenz
A strontium lattice clock with reduced blackbody radiation shift
oai:www.repo.uni-hannover.de:123456789/86892022-12-02T07:59:27Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
00925njm 22002777a 4500
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Baune, Christoph
author
2016
[no abstract]
Baune, Christoph: Frequency up-conversion of nonclassical states of light. Hannover : Gottfried Wilhelm Leibniz Universität Hannover, Diss., 2016, xi, 142 S.
https://www.repo.uni-hannover.de/handle/123456789/8689
http://dx.doi.org/10.15488/8636
Frequency up-conversion
squeezed light
entanglement
single photons
quantum non-Gaussianity
negative Wigner function
Frequenz-Hochkonversion
gequetschtes Licht
Verschränkung
Einzelphotonen
Quanten-Nichtgaußizität
negative Wignerfunktion
Frequency up-conversion of nonclassical states of light
oai:www.repo.uni-hannover.de:123456789/87142022-12-02T07:59:27Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
00925njm 22002777a 4500
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Denker, Timo
author
2016
[no abstract]
Denker, Timo: High-precision metrology with high-frequency nonclassical light sources. Hannover : Gottfried Wilhelm Leibniz Universität Hannover, Diss., 2016, xxii, 150 S.
https://www.repo.uni-hannover.de/handle/123456789/8714
http://dx.doi.org/10.15488/8661
Squeezed states
parametric oscillators
spectroscopy
Gequetschtes Licht
parametrischer Oszillator
Spektroskopie
High-precision metrology with high-frequency nonclassical light sources
oai:www.repo.uni-hannover.de:123456789/87462022-12-02T07:59:27Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
00925njm 22002777a 4500
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Händchen, Vitus
author
2016
[no abstract]
Händchen, Vitus: Experimental analysis of Einstein-Podolsky-Rosen steering for quantum information applications. Hannover : Gottfried Wilhelm Leibniz Universität Hannover, Diss., 2016, xii, 160 S.
https://www.repo.uni-hannover.de/handle/123456789/8746
http://dx.doi.org/10.15488/8693
Steering
squeezed light
quantum key distribution
Quantenlenkung
gequetschtes Licht
Quantenschlüsselverteilung
Experimental analysis of Einstein-Podolsky-Rosen steering for quantum information applications
oai:www.repo.uni-hannover.de:123456789/87712022-12-02T07:50:32Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
00925njm 22002777a 4500
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Kotzian, Monika
author
2016
[no abstract]
Kotzian, Monika: Path-resolved electron transport in a triangular triple quantum dot system. Hannover : Gottfried Wilhelm Leibniz Universität Hannover, Diss., 2016, 211 S.
https://www.repo.uni-hannover.de/handle/123456789/8771
http://dx.doi.org/10.15488/8718
Triple quantum dots
path-resolved transport
Coulomb correlations
Dreifachquantenpunkte
pfadaufgelöster Transport
Coulomb-Korrelationen
Path-resolved electron transport in a triangular triple quantum dot system
oai:www.repo.uni-hannover.de:123456789/87982022-12-02T07:54:06Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
00925njm 22002777a 4500
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Milsted, Ashley
author
2016
[no abstract]
Milsted, Ashley: Tensor network methods for quantum lattice systems. Hannover : Gottfried Wilhelm Leibniz Universität Hannover, Diss., 2015, x, 138 S.
https://www.repo.uni-hannover.de/handle/123456789/8798
http://dx.doi.org/10.15488/8745
Quantum lattice systems
tensor network states
nonabelian gauge theory
Quantengittersysteme
Tensornetzwerkzustände
nicht-abelsche Eichtheorie
Tensor network methods for quantum lattice systems
oai:www.repo.uni-hannover.de:123456789/88082022-12-02T07:54:06Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
00925njm 22002777a 4500
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Neukirchen, Bernhard
author
2016
[no abstract]
Neukirchen, Bernhard: Continuous time limit of repeated quantum observations. Hannover : Gottfried Wilhelm Leibniz Universität Hannover, Diss., 2015, xiv, 177 S.
https://www.repo.uni-hannover.de/handle/123456789/8808
http://dx.doi.org/10.15488/8755
Open quantum systems
delayed-choice quantum measurement
lindblad generators
Offene Quantensysteme
verzögerte Quantenmessung
Lindblad Erzeuger
Continuous time limit of repeated quantum observations
oai:www.repo.uni-hannover.de:123456789/88622022-12-02T19:35:27Zcom_123456789_11col_123456789_14doc-type:Articledoc-type:Textopen_accessddc:530status-type:publishedVersion
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Loriani, S.
author
Schlippert, D.
author
Schubert, C.
author
Abend, Sven
author
Ahlers, H.
author
Ertmer, Wolfgang
author
Rudolph, J.
author
Hogan, J.M.
author
Kasevich, M.A.
author
Rasel, E.M.
author
Gaaloul, N.
author
2019
Recent proposals for space-borne gravitational wave detectors based on atom interferometry rely on extremely narrow single-photon transition lines as featured by alkaline-earth metals or atomic species with similar electronic configuration. Despite their similarity, these species differ in key parameters such as abundance of isotopes, atomic flux, density and temperature regimes, achievable expansion rates, density limitations set by interactions, as well as technological and operational requirements. In this study, we compare viable candidates for gravitational wave detection with atom interferometry, contrast the most promising atomic species, identify the relevant technological milestones and investigate potential source concepts towards a future gravitational wave detector in space.
Loriani, S. et al.: Atomic source selection in space-borne gravitational wave detection. In: New Journal of Physics 21 (2019), Nr. 6, 063030. DOI: https://doi.org/10.1088/1367-2630/ab22d0
https://www.repo.uni-hannover.de/handle/123456789/8862
http://dx.doi.org/10.15488/8809
atom interferometry
general relativity
gravitational wave detection
inertial sensors
quantum gases
space physics
Atomic source selection in space-borne gravitational wave detection
oai:www.repo.uni-hannover.de:123456789/88962022-12-02T07:59:27Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
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Rudolph, Jan
author
2016
[no abstract]
Rudolph, Jan: Matter-wave optics with Bose-Einstein condensates in microgravity. Hannover : Gottfried Wilhelm Leibniz Universität Hannover, Diss., 2016, 198 S.
https://www.repo.uni-hannover.de/handle/123456789/8896
http://dx.doi.org/10.15488/8843
Bose-Einstein condensates
matter-waves
microgravity
Bose-Einstein Kondensate
Materiewellen
Mikrogravitation
Matter-wave optics with Bose-Einstein condensates in microgravity
oai:www.repo.uni-hannover.de:123456789/89102022-12-02T07:59:27Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
00925njm 22002777a 4500
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Schütte, Dirk
author
2016
[no abstract]
Schütte, Dirk: Modern control approaches for next-generation interferometric gravitational wave detectors. Hannover : Gottfried Wilhelm Leibniz Universität Hannover, Diss., 2016, xx, 159 S.
https://www.repo.uni-hannover.de/handle/123456789/8910
http://dx.doi.org/10.15488/8857
Modern control
cavity locking
autolocking
squeezed states
seismic isolation
Moderne Regelungstechnik
Resonatorstabilisierung
vollautomatische Regelung
gequetschte Zustände
seismische Isolierung
Modern control approaches for next-generation interferometric gravitational wave detectors
oai:www.repo.uni-hannover.de:123456789/89292022-12-02T07:59:27Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
00925njm 22002777a 4500
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Transchel, Fabian Wolfgang Günter
author
2016
[no abstract]
Transchel, Fabian Wolfgang Günter: On Monte Carlo time-dependent variational principles. Hannover : Gottfried Wilhelm Leibniz Universität Hannover, Diss., 2015, xv, 133 S.
https://www.repo.uni-hannover.de/handle/123456789/8929
http://dx.doi.org/10.15488/8876
Monte Carlo method
dissipative dynamics
Landblad equation
Monte-Carlo-Simulation
dissipative Dynamik
Lindblad-Gleichung
On Monte Carlo time-dependent variational principles
oai:www.repo.uni-hannover.de:123456789/89492022-12-02T07:59:27Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
00925njm 22002777a 4500
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Westphal, Tobias
author
2016
[no abstract]
Westphal, Tobias: A coating thermal noise interferometer for the AEI 10 m prototype facility. Hannover : Gottfried Wilhelm Leibniz Universität Hannover, Diss., 2016, XII, 247 S.
https://www.repo.uni-hannover.de/handle/123456789/8949
http://dx.doi.org/10.15488/8896
Brownian coating noise
interferometry
mirror suspendion
Brownsches Beschichtungsrauschen
Interferometrie
Spiegelaufhängung
A coating thermal noise interferometer for the AEI 10 m prototype facility
oai:www.repo.uni-hannover.de:123456789/89572022-12-02T07:59:27Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
00925njm 22002777a 4500
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Wimmer, Maximilian
author
2016
[no abstract]
Wimmer, Maximilian: Coupled nonclassical systems for coherent backaction noise cancellation. Hannover : Gottfried Wilhelm Leibniz Universität Hannover, Diss., 2016, xiv, 113 S., Seite xv-xxxviii
https://www.repo.uni-hannover.de/handle/123456789/8957
http://dx.doi.org/10.15488/8904
Quantum radiation pressure noise
coherent control
quantum control
nonclassical light
optomechanical cavities
coupled optical cavities
Quantenstrahlungsdruckrauschen
kohärente Rauschunterdrückung
Quantenkontrolle
nichtklassisches Licht
optomechanische Resonatoren
gekoppelte optische Resonatoren
Coupled nonclassical systems for coherent backaction noise cancellation
oai:www.repo.uni-hannover.de:123456789/89742022-12-02T07:54:06Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
00925njm 22002777a 4500
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Abend, Sven
author
2017
[no abstract]
Abend, Sven: Atom-chip gravimeter with Bose-Einstein condensates. Hannover : Gottfried Wilhelm Leibniz Universität Hannover, Diss., 2017, 172 S.
https://www.repo.uni-hannover.de/handle/123456789/8974
http://dx.doi.org/10.15488/8921
Bose-Einstein condensates
matter wave interferometry
gravimetry
Bose-Einstein Kondensate
Materiewelleninterferometrie
Gravimetrie
Atom-chip gravimeter with Bose-Einstein condensates
oai:www.repo.uni-hannover.de:123456789/89812022-12-02T07:54:06Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
00925njm 22002777a 4500
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Ast, Melanie
author
2017
[no abstract]
Ast, Melanie: Quantum-dense metrology for substraction of back-scatter disturbances in gravitational-wave detection. Hannover : Gottfried Wilhelm Leibniz Universität Hannover, Diss., 2017, 132 S.
https://www.repo.uni-hannover.de/handle/123456789/8981
http://dx.doi.org/10.15488/8928
Gravitational-wave detection
squeezed light
scattered light
two-mode-squeezing
quantum-dense metrology
Gravitationswellen-Detektion
gequetschtes Licht
Streulicht
zwei-Moden-gequetschtes Licht
quantendichte Messung
Quantum-dense metrology for substraction of back-scatter disturbances in gravitational-wave detection
oai:www.repo.uni-hannover.de:123456789/90062022-12-02T07:54:06Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
00925njm 22002777a 4500
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Černotík, Ondřej
author
2017
[no abstract]
Černotík, Ondřej: Novel approaches to optomechanical transduction. Hannover : Gottfried Wilhelm Leibniz Universität Hannover, Diss., 2017, xiii, 135 S.
https://www.repo.uni-hannover.de/handle/123456789/9006
http://dx.doi.org/10.15488/8953
Optomechanics
hybrid quantum systems
frequency conversion
Optomechanik
hybride Quantensysteme
Frequenzkonversion
Novel approaches to optomechanical transduction
oai:www.repo.uni-hannover.de:123456789/90692022-12-02T07:59:27Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
00925njm 22002777a 4500
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Lieser, Maike Danielle
author
2017
[no abstract]
Lieser, Maike Danielle: LISA optical bench development : experimental investigation of tilt-to-length coupling for a spaceborne gravitational wave detector. Hannover : Gottfried Wilhelm Leibniz Universität Hannover, Diss., 2017, 181 S.
https://www.repo.uni-hannover.de/handle/123456789/9069
http://dx.doi.org/10.15488/9016
LISA
gravitational wave detector in space
tilt-to-length coupling
imaging systems
Gravitationswellendetektor im Weltraum
Kopplung von Strahlverkippung in Weglängensignal
Abbildungssysteme
LISA optical bench development : experimental investigation of tilt-to-length coupling for a spaceborne gravitational wave detector
oai:www.repo.uni-hannover.de:123456789/90882022-12-02T07:59:27Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
00925njm 22002777a 4500
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Pachomow, Evgenij
author
2017
[no abstract]
Pachomow, Evgenij: One and two-color photoassociation spectroscopy of ultracold 40Ca. Hannover : Gottfried Wilhelm Leibniz Universität Hannover, Diss., 2017, 114 S.
https://www.repo.uni-hannover.de/handle/123456789/9088
http://dx.doi.org/10.15488/9035
Ultracold calcium atoms and molecules
one and two-color photoassociation spectroscopy
molecular ground-state potential
optical Feshbach resonances
scattering length
Ultrakalte Calcium-Atome und Calcium-Moleküle
Ein- und Zwei-Farben-Photoassoziationsspektroskopie
molekulares Grundzustand-Potenzial
optische Feshbach-Resonanzen
Streulänge
One and two-color photoassociation spectroscopy of ultracold 40Ca
oai:www.repo.uni-hannover.de:123456789/91042022-12-02T07:59:27Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
00925njm 22002777a 4500
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Rode, Johannes
author
2017
[no abstract]
Rode, Johannes: Twisted bilayers of folded graphene : morphology and electronic transport. Hannover : Gottfried Wilhelm Leibniz Universität Hannover, Diss., 2016, 284 S.
https://www.repo.uni-hannover.de/handle/123456789/9104
http://dx.doi.org/10.15488/9051
Twisted bilayer graphene
nanomachining
magnetotransport
Turbostratisches Bilagen-Graphen
mechanisches Nanostrukturieren
Twisted bilayers of folded graphene : morphology and electronic transport
oai:www.repo.uni-hannover.de:123456789/91172022-12-02T07:32:52Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
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Schuster, Sönke
author
2017
[no abstract]
Schuster, Sönke: Tilt-to-length coupling and diffraction aspects in satellite interferometry. Hannover : Gottfried Wilhelm Leibniz Universität Hannover, Diss., 2017, xiii, 229 S.
https://www.repo.uni-hannover.de/handle/123456789/9117
http://dx.doi.org/10.15488/9064
Interferometry
tilt-to-length coupling
LISA
Interferometrie
Kipp-zu-Längen Kopplung
Tilt-to-length coupling and diffraction aspects in satellite interferometry
oai:www.repo.uni-hannover.de:123456789/91862022-12-02T07:54:06Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
00925njm 22002777a 4500
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Scharnhorst, Nils
author
2018
[no abstract]
Scharnhorst, Nils: Multi-mode ground state cooling of trapped ions. Hannover : Gottfried Wilhelm Leibniz Universität Hannover, Diss., 2018, 53 S.
https://www.repo.uni-hannover.de/handle/123456789/9186
http://dx.doi.org/10.15488/9133
Clocks
laser stabilization
transfer-lock
ground state cooling
multimode ground state cooling
EIT cooling
double-bright EIT cooling
Uhren
Laserstabilisierung
Transferstabilisierung
Grundzustandskühlen
Multimodenkühlen
EIT Kühlen
Doppel EIT Kühlen
Multi-mode ground state cooling of trapped ions
oai:www.repo.uni-hannover.de:123456789/98562022-12-02T07:47:02Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
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Koch, Alexander
author
2020
The topic of this thesis is the initial link acquisition process for intersatellite laser interfer- ometers. Furthermore, a technique was studied that can be applied to enhance the signal to noise ratio of the established laser link. This work was carried out in the context of the Gravity Recovery And Climate Experiment Follow-On (GRACE-FO), Next Generation Gravity Field Mission (NGGM) and Laser Interferometer Space Antenna (LISA) satellite missions. Link acquisition is one of the most critical steps during the commissioning phase of an intersatellite laser interferometer. It is required to calibrate unknown pointing offsets of the laser beams that are caused by manufacturing and alignment tolerances of the instrument, structural distortions of the spacecraft (S/C) due to temperature changes and the different gravity levels on ground and in orbit, as well as insufficient knowledge about the attitude of the S/C. Furthermore, the frequencies of the lasers on the different S/C have to be matched to within the bandwidth of the opto-electronics readout chain. This thesis is split into two parts. The first part focuses on the Laser Ranging Interfer- ometer (LRI) on-board the GRACE-FO mission, while the second part is dedicated to future missions: LISA and NGGM, a possible successor to GRACE-FO. In the first part, laboratory tests that verified the robustness of the GRACE-FO link acquisition procedure are presented. These tests were carried out using a realistic mock-up LRI and a proper experimental test bed that allowed for the introduction of MHz Doppler frequency shifts, pW received (RX) laser powers and flat-top RX beams. Also shown in this part are analysis results of the actual in-orbit link acquisition process that was carried out in June 2018. Unambiguous laser beam pointing offsets below ±1 mrad and a frequency offset, also in the expected range, were obtained. Small alignment errors of the LRI’s triple mirror assemblies (TMAs) were studied by analyzing in-orbit data. A trade-off study is presented which shows how these errors can be optimally compensated by introducing dedicated beam pointing offsets.
In the second part of this thesis, the design, construction and characterization of an ex- perimental test bed that simulates the intersatellite laser link of LRI-like instrument is presented. The test bed faithfully recreates the RX laser power as function of the trans- mitted beam pointing angles with an error below 10 %, even for fast spatial scans of the TX beam. Furthermore, dedicated acquisition sensors were studied in the context of LISA and NGGM. A position sensitive photodetector (PSPD) and an indium gallium arsenide (InGaAs) camera with 256×320 pixels were investigated. The PSPD required a minimum laser power of ∼10 nW. The ratio of the achieved resolution, in terms of beamwalk on the sensor, to the sensor size was 0.2 %. Tests of the InGaAs camera were carried out with a laser power of 1 pW. The achieved resolution in relation to the sensor size was 0.065 %. Hence, both sensors fulfill the preliminary NGGM requirements, but only the InGaAs sensor satisfies all considered LISA requirements.
Koch, Alexander: Link acquisition and optimization for intersatellite laser interferometry. Hannover : Gottfried Wilhelm Leibniz Universität, Diss., 2020, xix, 181 S. DOI: https://doi.org/10.15488/9799
https://www.repo.uni-hannover.de/handle/123456789/9856
http://dx.doi.org/10.15488/9799
Laser Interferometry
Space instrumentation
Laserinterferometrie
GRACE Follow-On
Raumfahrt
Link acquisition and optimization for intersatellite laser interferometry
oai:www.repo.uni-hannover.de:123456789/99132022-12-02T07:47:02Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
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Dahlke, Veit
author
2020
In this thesis I present the results of photoassociation measurements in ensembles of
atomic calcium over an intensity range of below 1 W/cm2 up to 600 W/cm2. The temperature
of the atoms was reduced to 1 μK by laser and evaporative cooling. Afterwards
the two most-weakly bound states in the excited molecular potentials that dissociate
to the asymtote 3P1+1S0 have been investigated regarding the shape and absolute rate
of the resonances. The investigation showed that the measured rates differ by more
than an order of magnitude compared to theoretical calculations. The predictions are
based on a scattering formalism by Bohn & Julienne and wave functions derived from
coupled-channel calculations. The shape of the resonances, the width in particular,
agrees well with the numerical calculations. Especially the power broadening at high
intensity is reproduced by the experiment. Further the light shift introduced by the
photoassociation laser has been measured which also differs from the predictions.
In the further course of the thesis the numerical simulations were improved by considering
additional influences like the exact dependence of the Franck-Condon density and
the light shift of the photoassociation laser as a function of the collision energy. Additionally
the modeling of the experimental setup with a special emphasis on the volume
of the optical trap and thus the density of the atomic ensemble was improved and the
influence of varying trap depth and photoassociation duration has been studied. Investigating
possible explanations for the discrepancy of the measured rates compared to
theory, I show that by a modification of the coupling parameter and the spontaneous
decay rate of the molecular state the rates measured in the experiment can be reproduced
theoretically, with the restriction that at high intensity the calculated line shape
no longer agrees with the measurement. In the last chapter an improved experimental
apparatus is presented that by using an optical lattice suppresses thermal broadening
and thus simplifies the analysis substantially.
Dahlke, Veit: Photoassociation of 40Ca at high laser intensities. Hannover : Gottfried Wilhelm Leibniz Universität, Diss., 2020, VI, 100 S. DOI: https://doi.org/10.15488/9856
https://www.repo.uni-hannover.de/handle/123456789/9913
http://dx.doi.org/10.15488/9856
molecular physics
optical spectroscopy
photoassociation
ultracold atoms
spectral lineshapes
Spektroskopie
Molekülphysik
Laserkühlung
Photoassoziation
ultrakalte Atome
spektrale Linienformen
Photoassociation of 40Ca at high laser intensities
oai:www.repo.uni-hannover.de:123456789/98872022-12-02T07:47:02Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
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Hüper, Andreas
author
2020
Atom interferometers belong among today's most precise sensors and offer a broad range of possible metrological applications. Given their ability to measure accelerations and rotations precisely, they are suitable for inertial sensing, navigation and geodesy. Beyond this, they proved indispensible for time-keeping as well as fundamental research. This explains why the improvement of achievable sensitivities of atom interferometers is of particular interest. However the sensitivity of atom interferometers is fundamentally restricted by the standard quantum limit. The standard quantum limit can only be surpassed by employing entangled many-partice states. Entangled states, such as the twin-Fock state, allow atom interferometers to improve the phase sensitivity beyond the standard quantum limit, but they are reliant on an accurate detection of the interferometric out come.
In this work, an experimental apparatus is designed and set up that will allow for routine generation of highly entangled twin-Fock states in a Rubidium-87 spinor Bose-Einstein condensate.
As the main feature of this apparatus, an accurate atom counting fluorescence detection has been implemented. This detection achieves single-particle resolving fluorescence measurements for 1 up to 30 atoms. According to the noise analysis the single-atom resolution extends to a limiting atom number of 390(20) atoms. The implemented quadrupole coils with their strong gradient of up to 300 G/cm offer a tight confinement that in combination with the 55 W optical dipole trap laser will enable a fast repetition rate of the creation of highly entangled quantum states.
Hüper, Andreas: Accurate atom counting for entanglement-enhanced atom interferometry. Hannover : Gottfried Wilhelm Leibniz Universität, Diss., 2019, iv, 128 S. DOI: https://doi.org/10.15488/9830
https://www.repo.uni-hannover.de/handle/123456789/9887
http://dx.doi.org/10.15488/9830
accurate atom counting
entanglement-enhanced atom interferometry
single-atom resolution
Einzelatomauflösung
verschränkungsverstärkte Atominterferometrie
Akkurates Atomzählen
Accurate atom counting for entanglement-enhanced atom interferometry
oai:www.repo.uni-hannover.de:123456789/99872022-12-02T08:02:55Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
00925njm 22002777a 4500
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Zarantonello, Giorgio
author
2020
Trapped ions, together with superconducting qubits, are one of the two leading hardware platforms for scalable quantum information processing. The development of quantum computers represents a major technological breakthrough comparable to the introduction of classical computing. The benefits of this technology are currently limited by the technical capability to perform high fidelity entangling operations on the qubits. When gate fidelities surpass the fault-tolerance threshold it becomes possible, through error correction, to increase the system size to an arbitrary number of qubits. In this cumulative thesis we address some of the issues in the scalability of the trapped-ion quantum computer based on microwave near-fields. In this approach, gate operations on one or multiple ions are driven by an oscillating magnetic field generated by a current flowing through a conductor.
In the first part of this work we discuss the design of traps toward the implementation of large scale systems. We introduce the basic design of a surface-electrode ion trap with embedded microwave conductors. The oscillating magnetic field required to perform the operations is generated by a single optimized conductor. We discuss the simulation and characterization of the magnetic field pattern, which is fixed by the microwave conductor design. In addition, we demonstrate the capability to simulate, fabricate and characterize a multilayer surface ion trap. Multilayer traps are a key aspect for scalability since they are necessary to achieve large system sizes, with many `ion registers', where the registers are interconnected by physically transporting ions between them.
In the second part of this thesis we demonstrate the implementation of a two-qubit entangling gate and we explore the possibilities offered by quantum control methods to improve its fidelity. We perform an entangling gate on two 9Be+ ions and measure a Bell state fidelity of 98.2(1.2)%. Error characterization shows that the gate result is limited by technical issues connected to the ions' motional states. To reduce these errors we apply amplitude modulation of the gate microwave drive. After stabilization of the ions' radial modes, we obtain an amplitude modulated gate with infidelity in the 10^-3 range. The result is confirmed by analyzing the data using three different methods. Using additional dynamic decoupling techniques, these results could bring microwave near-field gates past the fault-tolerance threshold.
Zarantonello, Giorgio: Robust high fidelity microwave near-field entangling quantum logic gate. Hannover : Gottfried Wilhelm Leibniz Universität, Diss., 2020, viii, 124 S. DOI: https://doi.org/10.15488/9929
https://www.repo.uni-hannover.de/handle/123456789/9987
http://dx.doi.org/10.15488/9929
Trapped ions
Quantum information processing
Quantum computing
Microwaves near-field
Two-qubit gates
Quantum control
Amplitude modulation
Gefangene Ionen
Quanteninformationsverarbeitung
quanten-computing
Nahfeld-Mikrowellen
Zwei-Qubit Gatter
Quantenkontrolle
Amplitudenmodulation
Robust high fidelity microwave near-field entangling quantum logic gate
oai:www.repo.uni-hannover.de:123456789/100422022-12-02T08:12:01Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
00925njm 22002777a 4500
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Schmidt, Helena
author
2020
Gravity is well tested on several length scales, but some unified theories predict
deviations in the region below 1 mm. In this thesis I will present a method
to search for such deviations in the sub-micrometre length scale. Below 1 μm,
the electrostatic and the Casimir force are stronger than the gravitational
force by some magnitudes. To distinguish these forces, I have designed a new
force measurement setup based on the frequency modulation AFM technique.
Utilizing a quartz based parallelogram cantilever, it is feasible to measure
these forces with sufficient accuracy for us to set new constraints for possible
deviations of gravity. In this thesis I will present a new method of measuring
such deviations of gravity, and show the initial results I have obtained using it.
This will show that the measurement concept works, but that improvements
are necessary before we can achieve optimum measurement uncertainty.
Schmidt, Helena: Yukawa force spectroscopy to search for violations of Newton’s law of gravity below 1 μm distances. Hannover : Gottfried Wilhelm Leibniz Universität, Diss., 2020, 152 S. DOI: https://doi.org/10.15488/9983
https://www.repo.uni-hannover.de/handle/123456789/10042
http://dx.doi.org/10.15488/9983
Newton's law of Gravity
Casimir effect
Gravitation
Yukawa Potential
Casimir Effekt
Yukawa force spectroscopy to search for violations of Newton’s law of gravity below 1 μm distances
oai:www.repo.uni-hannover.de:123456789/101342022-12-02T07:32:52Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
00925njm 22002777a 4500
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Albers, Henning
author
2020
The precision of atom interferometers, targeted for example in the Hannover Very
Long Baseline Atom Interferometer (VLBAI) facility, imposes stringent requirements
in several respects. They concern the control of center-of-mass motion and expansion
of the wave packets by the matter-wave source as well as the number of atoms.
By reducing the expansion, systematic errors, appearing e.g. through wavefront
aberrations, can be lowered. These requirements can be matched by employing
ultracold quantum gases or even quantum degenerate gases. A promising method
to create those ensembles is evaporative cooling in a spatially modulated optical
dipole trap. Here, the utilization of time-averaged potentials enables the fast creation
of ultracold atomic ensembles with large number of atoms. Both, the higher
number of atoms and the increased repetition rate, enhance the performance of the
interferometer due to a lower quantum projection noise, which scales with 1/sqrt(N),
and a larger bandwidth of the sensor due to faster sampling. The shaping of the
matter-waves by techniques such as matter-wave lensing or Delta-Kick collimation
is also feasible due to the dynamic control of the trapping potential.
In this thesis the implementation and application of dynamic time-averaged optical
potentials created via center position modulation of dipole trap beams is
demonstrated. By evaporative cooling in these potentials, 1.9(0.4) x 10^5 condensed
atoms with an expansion temperature of 29.2(1.3) nK were achieved after 3 s of
evaporation. Up to 4.2(0.1) x 10^5 condensed atoms could be observed with slower
evaporation of 5 s. Subsequent matter-wave lensing is carried out yielding expansion
rates as low as 553(49) μms^-1 resulting in an effective temperature of 3.2(0.6) nK in
two dimensions. This lens can be applied at any stage of evaporative cooling, thus
short-cutting the generation of ultracold effective temperatures. In this thesis the
limitations of optical matter-wave lensing in the current setup are revealed and
ways to improve the performance are discussed.
The fast generation of ultracold atomic ensembles will enhance the performance of
the dual-species atom interferometer, which represents the experiment apparatus
for this thesis and strives for a test of the Universality of Free Fall with an uncertainty
on the order of 10^-9. The results of this thesis were used to test numerical
simulations which were utilized to show the perspective of generating up to 10^6
collimated condensed atoms within 1 s of cycle time in the rubidium source system
of Hannover’s VLBAI.
Albers, Henning: Time-averaged optical potentials for creating and shaping Bose-Einstein condensates. Hannover : Gottfried Wilhelm Leibniz Universität, Diss., 2020, xvii, 95 S. DOI: https://doi.org/10.15488/10073
https://www.repo.uni-hannover.de/handle/123456789/10134
http://dx.doi.org/10.15488/10073
time-averaged optical potentials
Bose-Einstein condensate
matter-wave lensing
zeitlich-gemittelte optische Potentiale
Bose-Einstein Kondensate
Materiewellen-Linse
Time-averaged optical potentials for creating and shaping Bose-Einstein condensates
oai:www.repo.uni-hannover.de:123456789/101472022-12-02T07:59:27Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
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Schwartz, Philip Klaus
author
2020
This thesis deals with the systematic treatment of quantum-mechanical systems situated in post-Newtonian gravitational fields. At first, we develop a framework of geometric background structures that define the notions of a post-Newtonian expansion and of weak gravitational fields. Next, we consider the description of single quantum particles under gravity, before continuing with a simple composite system. Starting from clearly spelled-out assumptions, our systematic approach allows to properly derive the post-Newtonian coupling of quantum-mechanical systems to gravity based on first principles. This sets it apart from other, more heuristic approaches that are commonly employed, for example, in the description of quantum-optical experiments under gravitational influence.
Regarding single particles, we compare simple canonical quantisation of a free particle in curved spacetime to formal expansions of the minimally coupled Klein–Gordon equation, which may be motivated from the framework of quantum field theory in curved spacetimes. Specifically, we develop a general WKB -like post-Newtonian expansion of the Klein–Gordon equation to arbitrary order in the inverse of the velocity of light. Furthermore, for stationary spacetimes, we show that the Hamiltonians arising from expansions of the Klein–Gordon equation and from canonical quantisation agree up to linear order in particle momentum, independent of any expansion in the inverse of the velocity of light.
Concerning the topic of composite systems, we perform a fully detailed systematic derivation of the first order post-Newtonian quantum Hamiltonian describing the dynamics of an electromagnetically bound two-particle system which is situated in external electromagnetic and gravitational fields. This calculation is based on previous work by Sonnleitner and Barnett, which we significantly extend by the inclusion of a weak gravitational field as described by the Eddington–Robertson parametrised post-Newtonian metric.
In the last, independent part of the thesis, we prove two uniqueness results characterising the Newton–Wigner position observable for Poincaré-invariant classical Hamiltonian systems: one is a direct classical analogue of the well-known quantum Newton–Wigner theorem, and the other clarifies the geometric interpretation of the Newton–Wigner position as ‘centre of spin’, as proposed by Fleming in 1965.
Schwartz, Philip Klaus: Post-Newtonian Description of Quantum Systems in Gravitational Fields. Hannover : Gottfried Wilhelm Leibniz Universität, Diss., 2020, xii, 133 S. DOI: https://doi.org/10.15488/10085
https://www.repo.uni-hannover.de/handle/123456789/10147
http://dx.doi.org/10.15488/10085
quantum systems under gravity
post-Newtonian expansion
post-Newtonian gravity
Quantensysteme unter Gravitation
post-Newton’sche Entwicklung
post-Newton’sche Gravitation
Post-Newtonian Description of Quantum Systems in Gravitational Fields
oai:www.repo.uni-hannover.de:123456789/102052022-12-02T07:59:27Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
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Loriani Fard, Sina Leon
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2020
The search for a fundamental, self-consistent theoretical framework to cover phenomena over all energy scales is possibly the most challenging quest of contemporary physics. Approaches to reconcile quantum mechanics and general relativity entail the modification of their foundations such as the equivalence principle. This corner stone of general relativity is suspected to be violated in various scenarios and is therefore under close scrutiny. Experiments based on the manipulation of cold atoms are excellently suited to challenge its different facets. Freely falling atoms constitute ideal test masses for tests of the universality of free fall in interferometric setups. Moreover, the superposition of internal energy eigenstates provides the notion of a clock, which allows to perform tests of the gravitational redshift. Furthermore, as atom interferometers constitute outstanding phasemeters, they hold the promise to detect gravitational waves, another integral aspect of general relativity. In recent years, atom interferometers have developed into versatile sensors with excellent accuracy and stability, and allow to probe physics at the interface of quantum mechanics and general relativity without classical analog.
In this thesis, various aspects regarding tests of general relativity with atom interferometry have been theoretically investigated. This includes the analysis of fundamental effects as well as feasibility studies of experimental configurations. The work is partially focussed on a space-borne mission scenario for a dedicated quantum test of the universality of free fall beyond state-of-the-art by dropping matter waves of different elements. To enable the target accuracy at the level of 10^(−17), a compensation scheme has been developed and discussed, mitigating the detrimental effects of imperfect test mass co-location upon release and relaxing the requirements on the source preparation by several orders of magnitude. In addition, it was demonstrated that the careful design of quantum degenerate sources is indispensable for these experiments, requiring tailored schemes to prepare miscible binary sources. The possibility to test the gravitational redshift with atom interferometers has also been examined in this thesis and connected to the ideas of clock interferometry. With the proof that closed light pulse atom interferometers without transitions between internal internal states are not sensitive to gravitational time dilation, an ongoing scientific debate has been resolved. Instead, certain configurations were shown to implement a quantum version of the special-relativistic twin paradox, for which an experiment has been proposed. Finally, requirements on atomic sources and atom optics for scenarios of gravitational wave detection on ground and in space have been investigated.
Loriani Fard, Sina Leon: Atom interferometry for tests of general relativity. Hannover : Gottfried Wilhelm Leibniz Universität, Diss., 2020, vii, 101 S. DOI: https://doi.org/10.15488/10142
https://www.repo.uni-hannover.de/handle/123456789/10205
http://dx.doi.org/10.15488/10142
atom interferometry
general relativity
equivalence principle
gravitational wave detection
Atominterferometrie
allgemeine Relativitätstheorie
Äquivalenzprinzip
Gravitationswellendetektion
Atom interferometry for tests of general relativity
oai:www.repo.uni-hannover.de:123456789/102062022-12-02T07:32:52Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
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Pook-Kolb, Daniel Klaus Ortwin
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2020
Marginally outer trapped surfaces (MOTSs) are the main tool in numerical relativity to infer properties of black holes in simulations of highly dynamical systems. On the one hand, the present work extends previous numerical methods in order to allow tracking of highly distorted horizons in axisymmetry. On the other hand, by applying the new method to a family of initial data as well as to simulations of head-on collisions of black holes, we discover three new phenomena: (i) the merger of MOTSs providing a connected history of the full merger in terms of marginal surfaces without any "jumps", (ii) the formation of self-intersecting MOTSs immediately after the merger, and (iii) a non-monotonicity result for the area of certain smoothly evolving MOTSs.
The merger of MOTSs closes a gap in our understanding of binary-black-hole mergers in terms of the quasilocal horizon framework and provides the quasilocal analog of the famous "pair-of-pants" picture of the event horizon of two merging black holes. It allows tracking the evolution of properties such as the area through the highly dynamical regimes from the initially separate to the final common horizon.
Through a detailed analysis of geometrical and dynamical properties, we uncover features of the horizons not often considered. In particular, we show why the area increase law for smoothly evolving MOTSs fails to hold in some of the cases analyzed here. Furthermore, we demonstrate a surprisingly direct correspondence of the decay behavior of multipoles and the shear on the outermost horizon with the quasinormal modes of a Schwarzschild black hole.
An important role is played by the spectrum of the MOTS stability operator, for which we provide numerical examples of the connection between invertibility of the operator and the existence of a MOTS. Furthermore, we give a prospect of how the full spectrum can become useful for gaining more insight into the merger in absence of symmetries.
Finally, a first working generalization of the new numerical algorithm to non-axisymmetric situations is shown, proving the general applicability of the method.
Pook-Kolb, Daniel Klaus Ortwin: Dynamical horizons in binary black hole mergers. Hannover : Gottfried Wilhelm Leibniz Universität, Diss., 2020, xi, 123 S. DOI: https://doi.org/10.15488/10143
https://www.repo.uni-hannover.de/handle/123456789/10206
http://dx.doi.org/10.15488/10143
dynamical horizons
black holes
numerical relativity
dynamische Horizonte
MOTS
Schwarze Löcher
numerische Relativitätstheorie
Dynamical horizons in binary black hole mergers
oai:www.repo.uni-hannover.de:123456789/102732022-12-02T07:59:27Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
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Momeni Pakdehi, Davood
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2020
The electrical quantum standards have played a decisive role in modern metrology, particularly since the introduction of the revised International System of Units (SI) in May 2019. By adapting the basic units to exactly defined natural constants, the quantized Hall resistance (QHR) standards are also given precisely. The Von Klitzing constant RK = h/e2 (h Planck's constant and e elementary charge) can be measured precisely using the quantum Hall effect (QHE) and is thus the primary representation of the ohm. Currently, the QHR standard based on GaAs/AlGaAs heterostructure has succeeded in yielding robust resistance measurements with high accuracy <10−9.
In recent years, graphene has been vastly investigated due to its potential in QHR metrology. This single-layer hexagonal carbon crystal forms a two-dimensional electron gas system and exhibits the QHE, due to its properties, even at higher temperatures. Thereby, in the future the QHR standards could be realized in more simplified experimental conditions that can be used at higher temperatures and currents as well as smaller magnetic fields than is feasible in conventional GaAs/AlGaAs QHR.
The quality of the graphene is of significant importance to the QHR standards application. The epitaxial graphene growth on silicon carbide (SiC) offers decisive advantages among the known fabrication methods. It enables the production of large-area graphene layers that are already electron-doped and do not have to be transferred to another substrate. However, there are fundamental challenges in epitaxial graphene growth. During the high-temperature growth process, the steps on the SiC surface bunch together and form terraces with high steps. This so-called step-bunching gives rise to the graphene thickness inhomogeneity (e.g., the bilayer formation) and extrinsic resistance anisotropy, which both deteriorate the performance of electronic devices made from it.
In this thesis, the process conditions of the epitaxial graphene growth through a so-called polymer-assisted sublimation growth method are minutely investigated. Atomic force microscopy (AFM) is used to show that the previously neglected flow-rate of the argon process gas has a significant influence on the morphology of the SiC substrate and atop carbon layers. The results can be well explained using a simple model for the thermodynamic conditions at the layer adjacent to the surface. The resulting control option of step-bunching on the sub-nanometer scales is used to produce the ultra-flat, monolayer graphene layers without the bilayer inclusions that exhibit the vanishing of the resistance anisotropy. The comparison of four-point and scanning tunneling potentiometry measurements shows that the remaining small anisotropy represents the ultimate limit, which is given solely by the remaining resistances at the SiC terrace steps.
Thanks to the advanced growth control, also large-area homogenous quasi-freestanding monolayer and bilayer graphene sheets are fabricated. The Raman spectroscopy and scanning tunneling microscopy reveal very low defect densities of the layers. In addition, the excellent quality of the produced freestanding layers is further evidenced by the four-point measurement showing low extrinsic resistance anisotropy in both micro- and millimeter-scales.
The precise control of step-bunching using the Ar flow also enables the preparation of periodic non-identical SiC surfaces under the graphene layer. Based on the work function measurements by Kelvin-Probe force microscopy and X-ray photoemission electron microscopy, it is shown for the first time that there is a doping variation in graphene, induced by a proximity effect of the different near-surface SiC stacks. The comparison of the AFM and low-energy electron microscopy measurements have enabled the exact assignment of the SiC stacks, and the examinations have led to an improved understanding of the surface restructuring in the framework of a step-flow model.
The knowledge gained can be further utilized to improve the performance of epitaxial graphene quantum resistance standard, and overall, the graphene-based electronic devices. Finally, the QHR measurements have been shown on the optimized graphene monolayers. In order to operate the graphene-based QHR at desirably low magnetic field ranges (B < 5 T), two known charge tuning techniques are applied, and the results are discussed with a view to their further implementation in the QHR metrology.
Keywords: Quantum resistance metrology, epitaxial graphene growth, silicon carbide, resistance anisotropy, argon flow-rate, homogenous quasi-freestanding graphene
Elektrische Quantennormale spielen eine wichtige Rolle in der modernen Metrologie, besonders seit der Einführung des revidierten Einheitensystems (SI) im Mai 2019. Durch die Zurückführung der Basiseinheiten auf exakt definierte Naturkonstanten sind auch die quantisierten Werte von Widerstandsnormalen (QHR) exakt gegeben. Die Von-Klitzing-Konstante RK = h/e2 (h Planck-Konstante und e Elementarladung) lässt sich mittels des Quanten-Hall-Effekts (QHE) präzise messen und ist somit die primäre Darstellung des Ohm. Die Quanten-Widerstandsnormale bestehen aktuell aus robusten GaAs/AlGaAs-Heterostrukturen, die eine Genauigkeit <10−9 für die Widerstands-Messung erlauben.
In den letzten Jahren wird verstärkt Graphen auf sein Potenzial für die Widerstandmetrologie untersucht. Der einlagige hexagonale Kohlenstoffkristall bildet ebenfalls ein zweidimensionales Elektrongas aus, das den Quanten-Hall-Effekt zeigt – und dies auf Grund seiner Eigenschaften schon bei höheren Temperaturen. Damit könnten in Zukunft Widerstandsnormale für vereinfachte experimentelle Bedingungen realisiert werden, die bei höheren Temperaturen und Strömen oder kleineren Magnetfeldern eingesetzt werden können, als es mit konventionellen GaAs/AlGaAs- QHR möglich ist.
Für den Einsatz als Widerstandsnormal ist die Qualität des Graphens von entscheidender Bedeutung. Unter den bekannten Herstellungsmethoden bietet das epitaktische Wachstum von Graphen auf Siliciumcarbid (SiC) entscheidende Vorteile. Es lassen sich damit großflächige Graphenschichten herstellen, die nicht auf ein anderes Substrat übertragen werden müssen. Allerdings gibt es grundlegende Herausforderungen beim epitaktischen Wachstum. So tritt bei hohen Prozesstemperaturen eine Bündelung der Kristallstufen auf der SiC-Substratoberfläche auf (Step-bunching), was zu einer bekannten extrinsischen Widerstandsanisotropie führt und darüber hinaus die Bildung von Bilagen-Graphen begünstigt. Beides verschlechtert die Eigenschaften der daraus hergestellten Widerstandsnormale.
In dieser Dissertation werden zunächst die Prozessbedingungen des mittels der sogenannten Polymer-Assisted-Sublimations-Growth-Methode hergestellten epitaktischen Graphens auf SiC genauer untersucht. Mithilfe der Rasterkraft-Mikroskopie (Atomic-Force-Microscopy, AFM) wird gezeigt, dass es einen erheblichen Einfluss der bisher wenig beachteten Flussrate des Prozessgases Argon auf die Morphologie des SiC-Substrates und der oberen Kohlenstoffschichten gibt. Anhand eines einfachen Modells für die thermodynamischen Verhältnisse in einer oberflächennahen Schicht lassen sich die Ergebnisse hervorragend erklären. Die sich daraus ergebende Kontrollmöglichkeit des Step-bunching auf Sub-Nanometer-Skalen wird genutzt, um ultraflache, monolagige Graphenschichten ohne Bilageneinschlüsse herzustellen, die eine verschwindende Widerstandsanisotropie aufweisen. Der Vergleich von Vierpunkt-Messungen und Scanning-Tunneling-Potentiometery-Messungen zeigt, dass die verbleibende geringe Anisotropie das ultimative Limit darstellt, die allein durch die verbleibenden Widerstände an den SiC-Terrassenstufen gegeben ist.
Dank der fortschrittlichen Wachstumskontrolle werden auch großflächige, homogene quasi-freistehende Monolage- und Bilage-Graphenschichten hergestellt. Die Raman-Spektroskopie und die Rastertunnel-Mikroskopie zeigen sehr geringe Defektdichten der Schichten. Darüber hinaus wird die hervorragende Qualität der hergestellten quasi-freistehenden Schichten durch die Vierpunkt-Messung unter Beweis gestellt, die eine geringe extrinsische Widerstandsanisotropie zeigt.
Die präzise Kontrolle des Step-bunching mittels Ar-Fluss ermöglicht auch die gezielte Präparation von periodischen, nicht-identischen SiC-Oberflächen unter der Graphenlage. Anhand von Messungen der Austrittsarbeit mit Kelvin-Probe-Force-Microscopy und X-ray Photoemission-Electron-Microscopy konnte erstmals gezeigt werden, dass es eine Variation der Graphendotierung, induziert durch einen Proximity Effekt der unterschiedlichen oberflächennahen SiC-Stapel, gibt. Der Vergleich von AFM und Low-Energy-Electron-Microscopy-Messungen ermöglicht die genaue Zuordnung der SiC-Stapel und die Untersuchungen führen insgesamt zu einem verbesserten Verständnis der Oberflächen-Umstrukturierung im Rahmen eines adäquaten Step-Flow-Modells.
Die gesammelten Erkenntnisse können zur Verbesserung der Eigenschaften von Graphen-Quantennormalen und auch allgemein von graphenbasierten Bauteilen genutzt werden. Abschließend werden QH-Widerstandsmessungen an optimierten Graphen-Monolagen gezeigt. Um den Magnetfeldbereich (B < 5 T) einzuschränken, werden zwei bekannte extrinsische Dotiertechniken verwendet und die Ergebnisse werden im Hinblick auf den weiteren Einsatz in der QH-Metrologie diskutiert.
Schlüsselwörter: Wachstum des epitaktischen Graphens, Siliciumcarbid, Argon-Flussrate, Widerstandsanisotropie, homogenes quasi-freistehendes Graphen
Momeni Pakdehi, Davood: Optimization of epitaxial graphene growth for quantum metrology. Hannover : Gottfried Wilhelm Leibniz Universität, Diss., 2020, v, 213 S. DOI: https://doi.org/10.15488/10201
https://www.repo.uni-hannover.de/handle/123456789/10273
http://dx.doi.org/10.15488/10201
epitaxial graphene growth
homogenous quasi-freestanding graphene
Quantum resistance metrology
argon flow-rate
resistance anisotropy
SiC
silicon carbide
polymer-assisted sublimation growth
Wachstum des epitaktischen Graphens
homogenes quasi-freistehendes Graphen
Siliciumcarbid
Stacking-order
Polarization doping
Argon-Flussrate
Widerstandsanisotropie
Optimization of epitaxial graphene growth for quantum metrology
oai:www.repo.uni-hannover.de:123456789/102682022-12-02T07:59:27Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
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Matthias, Jonas
author
2020
In the past century, the development of gravimeters with low uncertainty and long-term stability has led to new fields of research in geodesy and geoscience. Decreasing the instrumental measurement uncertainty further will enable observations of previously inaccessible phenomena, for instance, mass transport in hydrology and volcanology. During the last decades, quantum sensors based on the interference of cold atoms have been developed. Using a cold atomic gas as test mass, the accuracy of these sensors is not limited by mechanical properties but by effects caused by the thermal expansion of the atomic ensemble. The application of ultra-cold atomic ensembles with lower expansion rates in atom interferometer gravimeters is projected to reduce the leading order uncertainties by more than an order of magnitude. At the same time, atom chip technology makes it possible to prepare ultra-cold atomic ensembles at a high repetition rate and to miniaturise the sensor size. These advancements promise the realisation of an absolute gravimeter with unprecedented accuracy.
This thesis describes the design considerations and the assembly of the transportable Quantum Gravimeter (QG-1) based on light-pulse atom interferometry of Bose-Einstein condensates (BEC) prepared on an atom chip. It is estimated, that the two leading order uncertainties of systematic biases governing the instrumental measurement uncertainty of current generation cold atom gravimeters are reduced to less than 1 nm/s² in the QG-1 apparatus. The established design of an atom-chip-based BEC source pioneered in the Quantus collaboration is modified to meet the requirements of QG-1. A free optical aperture of 18 mm for the interferometry laser beam is realised by changing the orientation of the atom-chip-based BEC source. Therefore, a new layout of the mesoscopic wire structure of the atom chip is required. The design described in this thesis enables atom interferometry with a free falling test mass with a baseline of 330 mm. The retro-reflection mirror is placed inside the vacuum chamber to eliminate optical elements in the atom interferometer beam path. It is mounted on a custom designed tip/tilt-stage with compact size and a large dynamic range of up to a hundredfold of the Earth's rotation rate for characterisation. Furthermore, a compact, robust and transportable fibre based laser system with modular electronics and a computer control system are set up.
The key result of this thesis is the reliable operation of the ultra-cold atomic source on the atom chip. After optimisation of the trap loading procedure for a high atom number and low excitation of oscillations, it was shown that the necessary design change of the atom chip allows for efficient operation. The compressed magnetic trap has a geometrically averaged trap frequency of 2π · 256 Hz and the trapped ensemble has a lifetime of 3.2 s. The evaporative cooling procedure starts with 3.3 · 10⁷ atoms at a temperature of 166 μK. Within 1.3 s, or 2.3 s for the complete sequence, 3000 atoms are prepared at a temperature of 160 nK close to the critical temperature for Bose-Einstein condensation.
Matthias, Jonas: Magnetic trapping for an atom-chip-based gravimeter. Hannover : Gottfried Wilhelm Leibniz Universität, Diss., 2020, III, 95 S. DOI: https://doi.org/10.15488/10196
https://www.repo.uni-hannover.de/handle/123456789/10268
http://dx.doi.org/10.15488/10196
atom chip
atom interferometry
gravimetry
Atomchip
Atominterferometrie
Gravimetrie
Magnetic trapping for an atom-chip-based gravimeter
oai:www.repo.uni-hannover.de:123456789/102872022-12-02T07:32:52Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
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Lachmann, Maike Diana
author
2020
Hochpräzise Atominterferometrie mit Bose-Einstein-Kondensaten hat das Potential Tests fundamentaler Physik mit bisher unerreichter Genauigkeit durchzuführen, sowie die Entwicklung neuartiger Sensoren für die Erdbeobachtung zu initiieren. Insbesondere schaffen Messungen mit Atominterferometern im Weltraum den Rahmen für Tests der allgemeinen Relativitätstheorie, der Suche nach dunkler Energie, satellitengestützter Erdbeobachtung und der Detektion von Gravitationswellen in einem auf der Erde nicht erreichbaren Regime. Die technischen Ansprüche einer Weltraummission unterscheiden sich grundlegend von denen eines Laboraufbaus. Neben einer Optimierung bezüglich der Masse, der Leistungsaufnahme und des Volumens muss die Apparatur autonom und wartungsfrei arbeiten, sowie robust gegen Vibrationen und Beschleunigungen während des Aufstiegs und Wiedereintritts in die Atmosphäre sein.
Mit der MAIUS-1 Mission ist es am 23.01.2017 zum ersten Mal gelungen Bose-
Einstein-Kondensate im Weltraum zu erzeugen. Erstmals wurde eine solche Apparatur an Bord einer Höhenforschungsrakete betrieben und hat Schlüsselmethoden für präzise Materiewelleninterferometrie demonstriert. In den insgesamt 13 Minuten des Parabelfluges befand sich die Nutzlast sechs Minuten lang über bei einer Höhe von 100km unter Mikrogravitationsbedingungen.
Während des Starts und Aufstiegs konnten für eine Minute Experimente zum Kühlen und Fangen kalter atomarer Ensembles in dieser hochdynamischen Umgebung durchgeführt werden.
In der Mikrogravitationsphase wurde der Phasenübergang zum Bose-Einstein-
Kondensat mit mehr als 105 Rubidiumatomen untersucht. Die Präparation der
ultrakalten Ensembles für die Interferometrie wurde charakterisiert und autonom
vom System optimiert, wobei sich die Reproduzierbarkeit aller Prozesse zur Kühlung zeigte. Des Weiteren wurden Zwei-Photonen-Prozesse genutzt, um die Materiewelle in die Superposition von Impulszuständen zu überführen und zur Interferenz zu bringen. Somit konnte die Kohärenz über die gesamte Ausdehnung der Kondensate nachgewiesen werden. Mit jeder Licht-Materie-Wechselwirkung wurde eine zusätzliche Phasenmodulation auf die Materiewelle aufgeprägt. Diese Struktur wurde nach einer freien Evolutionszeit in der räumlichen Dichteverteilung sichtbar und konnte für weitere Analysen verschiedener Spinorkomponenten des Ensembles verwendet werden.
Die Erkenntnisse zur Präparation der ultrakalten Ensembles und zur Interferometrie
im Weltraum wie auch die entwickelten Technologien ermöglichen künftige Missionen.
Lachmann, Maike Diana: Materiewelleninterferenzen im Weltraum. Hannover : Gottfried Wilhelm Leibniz Universität, Diss., 2020, vii, 128 S. DOI: https://doi.org/10.15488/10215
https://www.repo.uni-hannover.de/handle/123456789/10287
http://dx.doi.org/10.15488/10215
Bose-Einstein condensation
atom interferometry
space
Bose-Einstein-Kondensation
Atominterferometrie
Weltraum
Materiewelleninterferenzen im Weltraum
oai:www.repo.uni-hannover.de:123456789/103392023-04-06T10:03:09Zcom_123456789_1com_123456789_11col_123456789_7col_123456789_14doc-type:BookPartdoc-type:Textopen_accessstatus-type:publishedVersionddc:620
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Steinecke, Morten
author
Kellermann, Tarik
author
Jupé, Marco
author
Ristau, Detlev
author
Jensen, Lars
author
2018
The exploitation of nonlinear effects in multi-layer thin films allows for optics with novel functions, such as all-optical switching and frequency conversion. In this contribution, an improved interferometric setup for the measurement of the nonlinear refractive index in dielectric substrates and deposited single layers is presented. The setup is based on the wave front deformation caused by the self-focusing in the measured samples. Additionally, measurement results for a highly nonlinear material, indium-Tin-oxide (ITO) are presented with respect to the materials power handling capabilities and compared to values from other materials. © COPYRIGHT SPIE
Steinecke, M.; Kellermann, T.; Jupé, M.; Ristau, D.; Jensen, L.: Measurement setup for the determination of the nonlinear refractive index of thin films with high nonlinearity. In: Proceedings of SPIE 10805 (2018), 1080524. DOI: https://doi.org/10.1117/12.2500341
https://www.repo.uni-hannover.de/handle/123456789/10339
http://dx.doi.org/10.15488/10266
Kerr-effect
Material science
Nonlinear optics
Self-focusing
Thin films
Measurement setup for the determination of the nonlinear refractive index of thin films with high nonlinearity
oai:www.repo.uni-hannover.de:123456789/104272022-12-02T07:59:27Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
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Schulte, Marius
author
2020
This thesis describes new results on the entanglement of atomic spins in Ramsey interferometry, optical atomic clocks and trapped ions.
It is divided into three parts:
First, we investigate improvements to conventional Ramsey interferometry with entanglement and adding only rotations of the collective spin to adjust the signal and measurement directions.
The geometric degrees of freedom, connected to the rotations, are analytically optimized for a large class of generalized Ramsey protocols to allow efficient optimization of all parameters.
Besides a unification of existing approaches, the main result is that there is only one new protocol, where a previously unused double inversion is applied.
Studies of the local sensitivity show that this protocol reaches the fundamental quantum Fisher information limit and is yet robust against errors during preparation and measurement.
In the second section we investigate the conditions under which optical atomic clocks exhibit increased long-term stability when applying weakly entangled, spin squeezed states. We discuss the common case of an atomic clock with a single ensemble, typical Brownian frequency noise and finite dead time. Theoretical modelling of the servo loop allows quantitative predictions of the optimal stability for given values of dead time and laser noise, in very good agreement with numerical simulations of the closed feedback loop.
The main result is that, even with the current most stable lasers, the clock stability can only be improved for ensembles below a critical atom number of about one thousand in optical Sr lattice clocks.
Even with a future improvement of the laser performance by one order of magnitude, the critical atom number still remains below 100,000.
In contrast, clocks based on smaller, non-scalable ensembles, such as ion clocks, can already benefit from squeezed states with current clock lasers.
Thus the last section considers the robust generation of entanglement in ion traps. An error budget including relevant experimental error sources is calculated for state-of-the-art quantum gates, driven by oscillating microwave gradients in surface traps. Amplitude modulation of the driving fields is shown to efficiently counteract the current limitations from motional mode instability. The predicted increase of the gate quality was demonstrated by the group of C. Ospelkaus at PTB Braunschweig, who measured gates with errors as low as ~ 10^(-3).
In a similar approach, interactions between spin and motion can also be generated by combining oscillating rf-fields with a static magnetic field gradient. Penning traps designed for precision spectroscopy already feature large magnetic field gradients at the edge of a magnetic bottle configuration. We present parameters and conditions under which laser-free coupling of spin and quantized motion for (anti-)protons is possible at these points, in a step towards quantum logic spectroscopy for (anti-)protons.
Schulte, Marius: Entanglement in Ramsey interferometry, optical atomic clocks and trapped ions. Hannover : Gottfried Wilhelm Leibniz Universität, Diss., 2020, xii, 179 S. DOI: https://doi.org/10.15488/10353
https://www.repo.uni-hannover.de/handle/123456789/10427
http://dx.doi.org/10.15488/10353
quantum metrology
entanglement
Ramsey interferometry
spin squeezing
optical atomic clocks
trapped ions
two-qubit gates
Quantenmetrologie
Verschränkung
Ramsey Interferometrie
gequetschte Spinzustände
optische Atomuhren
gefangene Ionen
Zwei-qubit Gatter
Entanglement in Ramsey interferometry, optical atomic clocks and trapped ions
oai:www.repo.uni-hannover.de:123456789/108502022-12-02T07:59:27Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
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Feldmann, Polina
author
2021
Entanglement lies at the core of emergent quantum technologies such as quantum-enhanced metrology, quantum communication and cryptography, and quantum simulation and computing. Spinor Bose-Einstein condensates (BECs) offer a promising platform for the generation and application of entangled states. For example, a spin-1 BEC has served for the proof-of-principle demonstration of a quantum-enhanced atomic clock. Ferromagnetic spin-1 BECs with zero magnetization exhibit three ground-state quantum phases with different entanglement properties. The control parameter can be tuned by a magnetic field or by microwave dressing. As already experimentally demonstrated, an entangled ground state can be reached from a well accessible, non-entangled one by driving the control parameter across quantum phase transitions (QPTs).
We investigate which of the entangled ground states afford quantum-enhanced interferometry. The interferometric usefulness is quantified by the quantum Fisher information (QFI), which we analyze throughout all ground-state phases. A large QFI at about half the Heisenberg limit, and thus far above the standard quantum limit, is attained by the well-known Twin-Fock state and by the central broken-axisymmetry (CBA) state. We detail how the CBA state can be used as a probe for quantum-enhanced interferometry.
Furthermore, we observe that the large QFI of the CBA state can be traced back to enclosed macroscopic superposition states (MSSs). Measuring the atom number in one out of three modes generates, with high probability and heralded by the measurement outcome, a MSS similar to a NOON state. Our proposal promises NOON-like MSSs of unprecedentedly many atoms.
Both proposed applications of the adiabatically prepared CBA state depend only on existent technology. Our numerical results show that they tolerate a reasonably swift quasiadiabatic passage in the presence of atom loss as well as uncertainties of atom counting.
Excited-state quantum phase transitions (ESQPTs) extend the concept of QPTs beyond the ground state. While they have been extensively investigated theoretically, there are only few experimental results. From the perspective of quantum-state engineering, it is furthermore surprising how rarely order parameters of ESQPTs are discussed in the literature. Mean-field models for spinor BECs imply ESQPTs, to which some experimental observations on the mean-field dynamics can be attributed. However, so far, neither theoretical nor experimental studies have specifically addressed ESQPTs in spinor BECs.
We extend the ground-state phase diagram of ferromagnetic spin-1 BECs with zero magnetization across the spectrum. There are three excited-state phases, corresponding to one ground-state phase each. The ESQPTs are signaled by a diverging density of states. The mean-field phase-space trajectories can be characterized by a winding number that is in one-to-one correspondence to the excited-state phases. We derive a closely related order parameter encoded in the dynamics of coherent states and discuss how this order parameter can be interferometrically measured in current experiments. Remarkably, the mean-field model governing the ESQPTs in spin-1 BECs with zero magnetization is encountered also, e. g., in molecular and nuclear physics. Because of the superior experimental control, spinor BECs can be considered as simulators of the ESQPTs in those systems.
Our results contribute to quantum-state engineering and quantum-enhanced interferometry in spinor BECs and to the characterization of excited-state quantum phases. The latter may, in turn, lead on to applications in quantum-state engineering.
Feldmann, Polina: Generalized quantum phase transitions for quantum-state engineering in spinor bose-einstein condensates. Hannover : Gottfried Wilhelm Leibniz Universität, Diss., 2021, 131 S. DOI: https://doi.org/10.15488/10772
https://www.repo.uni-hannover.de/handle/123456789/10850
http://dx.doi.org/10.15488/10772
quantum-state engineering
spinor Bose-Einstein condensates
ground-state quantum phase transitions
excited-state quantum phase transitions
order parameters
quantum-enhanced metrology
quantum-enhanced interferometry
macroscopic superposition states
Fisher information
mean-field convergence
Verschränkte Quantenzustände
Quantenphasenübergänge
Bose-Einstein-Kondensate
Quantenmetrologie
Generalized Quantum Phase Transitions for Quantum-State Engineering in Spinor Bose-Einstein Condensates
oai:www.repo.uni-hannover.de:123456789/111422022-12-02T07:32:52Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
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Idel, Alexander
author
2021
Quantum Sensors, like atom interferometers (AI), can be employed for
high-precision measurements of inertial forces, including their application
as gravimeters, gradiometers, accelerometers, and gyroscopes.
Their measurement principle relies on ultracold atoms that are prepared
in quantum-mechanical superposition states in external degrees
of freedom. These states can be prepared by a momentum transfer of
a Raman laser. Then the superposition state senses the effect of an inertial
force, which induce a corresponding relative phase. The phase is
read out by a final coupling which converts the interferometric phase
into a atom number difference between the two states. The difference
provides an estimate of the interferometric phase and the corresponding
quantity of interest. The quantum mechanical noise of the atomic
ensemble cause a fundamental uncertainty of this estimation, which I
analyze for generic AIs. For small atomic densities, the quantum phase
noise of the ensemble limits the interferometric sensitivity. For large
densities, quantum number fluctuations generate density fluctuations,
which generates phase noise. I show that these two competing effects
result in an optimal atom number with a maximal interferometer resolution.
Squeezed atomic samples allow for a reduction of the quantum
noise of one quantity at the expense of an increased noise along of a
conjugate quantity. Phase and number are such quantities which obey
to a variant of Heisenberg’s uncertainty principle. Neither phase nor
number squeezing can improve the maximal interferometer resolution.
As one main result of this thesis, I show how an optimal squeezing
in between number and phase squeezing, allows for a fundamental
improvement. I evaluate possible experimental paths to implement
the proposed protocol.
Concepts for a squeezing-enhanced operation of external-degree
AIs have not yet been demonstrated. I propose and implement an
atomic gravimeter, which is designed to accept spin-squeezed atomic
states as input states. The interferometer is designed such that the
interferometer couplings are performed in spin space, while the phase
accumulation is performed in momentum states. For this interferometer,
the squeezed input can be directly obtained from spin dynamics
in spinor Bose-Einstein condensates. The main noise contributions in
the experiment are analyzed, which results in a factor of 84 above
the relevant quantum limit, preventing a squeezing enhancement so
far. I outline a suppression of the main noise source, uncontrolled
AC Stark shift on the squeezed mode and propose future important
applications, including test of spontaneous collapse theories and an
improvement of large-scale, high-precision gradiometers.
Idel, Alexander: Entanglement for atom interferometers. Hannover : Gottfried Wilhelm Leibniz Universität, Diss., 2021, x, 101 S. DOI: https://doi.org/10.15488/11060
https://www.repo.uni-hannover.de/handle/123456789/11142
http://dx.doi.org/10.15488/11060
entanglement
atom optic
atom interferometry
Verschränkung
Atomoptik
Atominterferometrie
Entanglement For Atom Interferometers
oai:www.repo.uni-hannover.de:123456789/110962022-12-02T07:32:52Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
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Piest, Baptist
author
2021
Im Rahmen dieser Arbeit wird die atomchipbasierte Experimentierkammer für den Einsatz
in den Höhenforschungsraketenmissionen MAIUS-2 und 3 aufgebaut und mit einem bodengestützten
System in Betrieb genommen. Die neue Apparatur ermöglicht innerhalb von
3.4 s die Erzeugung von Bose-Einstein-Kondensaten mit 3*10E5 Rb-87 Atomen oder 6*10E4
K-41 Atomen. Zusätzlich können quantenentartete Mischungen mit variablen Isotopenverhältnissen
bereitgestellt werden. In Untersuchungen zur sympathetischen Kühlung von
K-41 durch Rb-87 wird der Einfluss der Gravitation auf Thermalisierungsraten quantifiziert.
Das Expansionsverhalten frei fallender Bose-Einstein-Kondensate wird für beide Isotope
untersucht. Transiente Magnetfelder während des Ausschaltens der Magnetfalle zeigen
dabei einen erheblichen Einfluss auf die Expansion und müssen in Simulationen berücksichtigt
werden. Im Rahmen der Analyse kollektiver Anregungen reiner und gemischter
Kondensate kann eine gegenseitige Dämpfung der Anregungen aufgrund der gegenseitigen
Wechselwirkung aufgezeigt werden. Schließlich wird der Einfluss der Gravitation auf den
Grundzustand und die Massenschwerpunktsbewegung der wechselwirkenden Ensembles
durch Rotation der Apparatur in Flugzeitmessungen untersucht.
This thesis presents the next generation atom chip apparatus for the sounding rocket
missions MAIUS-2 and -3. With the new apparatus, Bose-Einstein condensates containing
3 · 10E5 atoms of Rb-87 or 6 · 10E4 atoms of K-41 are generated within 3.4 s in ground-based
operation. In addition, quantum degenerate mixtures with variable isotope ratios can be
provided. An analysis of sympathetic cooling of K-41 under the influence of gravity and
prospects for thermalization rates in microgravity are given. The expansion dynamics of
single species Bose-Einstein condensates released from a magnetic trap is analyzed in detail.
It is shown that transient magnetic fields during trap switch-off have a considerable impact
on the expansion dynamics. Further, collective excitations of single and mixed ensembles
are evaluated. Due to interspecies damping, collective excitations of interacting mixtures
of K-41 and Rb-87 are strongly suppressed. Finally, the influence of gravity on a trapped
and strongly interacting mixture is observed via rotation of the whole apparatus.
Piest, Baptist: Bose-Einstein condensation of K-41 and Rb-87 on an atom chip for sounding rocket missions. Hannover : Gottfried Wilhelm Leibniz Universität, Diss., 2021, iii, 112 S. DOI: https://doi.org/10.15488/11014
https://www.repo.uni-hannover.de/handle/123456789/11096
http://dx.doi.org/10.15488/11014
Bose-Einstein condensates
quantum-degenerate mixtures
microgravity
space
Bose-Einstein Kondensate
quantenentartete Mischungen
Mikrogravitation
Weltraum
Bose-Einstein condensation of K-41 and Rb-87 on an atom chip for sounding rocket missions
oai:www.repo.uni-hannover.de:123456789/111322022-12-02T07:59:27Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
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Bondarenko, Dmytro
author
2021
Entangled possibly mixed states are an essential resource for quantum computation, communication, metrology, and the simulation of many-body systems. It is important to develop and improve preparation protocols for such states.
One possible way to prepare states of interest is to design an open system that evolves only towards the desired states. A Markovian evolution of a quantum system can be generally described by a Lindbladian. Tensor networks provide a framework to construct physically relevant entangled states. In particular, matrix product density operators (MPDOs) form an important variational class of states. MPDOs generalize matrix product states to mixed states, can represent thermal states of local one-dimensional Hamiltonians at sufficiently large temperatures, describe systems that satisfy the area law of entanglement, and form the basis of powerful numerical methods. In this work we develop an algorithm that determines for a given linear subspace of MPDOs whether this subspace can be the stable space of some frustration free k-local Lindbladian and, if so, outputs an appropriate Lindbladian.
We proceed by using machine learning with networks of quantum channels, also known as quantum neural networks (QNNs), to train denoising post-processing devices for quantum sources. First, we show that QNNs can be trained on imperfect devices even when part of the training data is corrupted. Second, we show that QNNs can be trained to extrapolate quantum states to, e.g., lower temperatures. Third, we show how to denoise quantum states in an unsupervised manner. We develop a novel quantum autoencoder that successfully denoises Greenberger-Horne-Zeilinger, W, Dicke, and cluster states subject to spin-flip, dephasing errors, and random unitary noise.
Finally, we develop recurrent QNNs (RQNNs) for denoising that requires memory, such as combating drifts. RQNNs can be thought of as matrix product quantum channels with a quantum algorithm for training and are closely related to MPDOs.
The proposed preparation and denoising protocols can be beneficial for various emergent quantum technologies and are within reach of present-day experiments.
Bondarenko, Dmytro: Constructing networks of quantum channels for state preparation. Hannover : Gottfried Wilhelm Leibniz Universität, Diss., 2021, 185 S. DOI: https://doi.org/10.15488/11050
https://www.repo.uni-hannover.de/handle/123456789/11132
http://dx.doi.org/10.15488/11050
denoising
state preparation
open quantum systems
quantum machine learning
dissipative preparation
quantum state engineering
parent Lindbladians
matrix product density operators
quantum neural networks
recurrent quantum neural networks
quantum autoencoders
quantum channels
quantum state extrapolation
Rauschunterdrückung
Zustandspräparation
offene Quantensysteme
maschinelles Lernen auf Quantencomputern
Quantendaten
dissipative Zustandspräparation
Design von Quantenzuständen
erzeugende Lindbladoperatoren
Matrixproduktdichteoperator
Neuronale Netze auf Quantencomputern
Quantenautoencoder
Quantenkanäle
Extrapolation von Quantenzuständen
Constructing networks of quantum channels for state preparation
oai:www.repo.uni-hannover.de:123456789/111782022-12-02T07:47:02Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
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Kiethe, Jan
author
2021
Trapped ion Coulomb crystals are regularly used as analogue simulators for physical systems, for which the access to the dynamics of the individual particles is lacking or which are hard to simulate using classical computers. One area of interest are solid-state friction models with two atomically flat surfaces sliding against each other. Typically, the access to the dynamics of the individual particles is lacking in realistic interfaces, therefore, ion crystals have been proposed in order to test friction models. While a model system of an ion chain sliding over a rigid optical potential has been demonstrated, a model system that implements back action between the two sliding surfaces does not exist.
In this cumulative thesis, an atomic system with intrinsic back action and access to individual particles that allows the study of nanofriction is presented. The system consists of an ion Coulomb crystal in the two-dimensional zigzag phase, into which a topological defect is introduced. The defect leads to a mismatch between the ion chains, which allows for the observation of the pinning-to-sliding phase transition for a finite system. The transition shows symmetry breaking and the existence of a soft mode at zero temperature, which is a localized topological defect mode. The influence of the defect's position and type on the existence of the soft mode is studied. It is found that breaking the intrinsic symmetry of the topological defect in the sliding phase by external forces prevents the observation of the soft mode.
In the presented experiments, mode frequencies are determined with resonant excitation of the collective motions of the ions via amplitude modulation of a Doppler cooling laser. A non-zero soft mode frequency at the transition is measured, which is attributed to the finite crystal temperature.
Furthermore, the linear-to-zigzag transition and the zigzag mode, i.e., the soft mode of this transition, under thermal noise are investigated. An increase in the mode frequency with temperature, as well as fast switching between the two possible ground states of the two-dimensional zigzag phase is found. An analytical model is derived that explains the observed temperature dependence of the low-frequency spectrum at the linear-to-zigzag transition. This analysis has important consequences for the cooling of a soft mode near a symmetry-breaking transition. In the future, this model could be adaptable to the pinning-to-sliding transition in order to further the understanding of the thermal effects of friction and heat transport.
Kiethe, Jan: Atomic friction and symmetry-breaking transitions in ion coulomb systems. Hannover : Gottfried Wilhelm Leibniz Universität, Diss., 2021, iii, 72 S. DOI: https://doi.org/10.15488/11095
https://www.repo.uni-hannover.de/handle/123456789/11178
http://dx.doi.org/10.15488/11095
Coulomb crystals
nanofriction
phase transitions
symmetry breaking
topological defects
Coulomb Kristalle
Nanoreibung
Phasenübergänge
Symmetriebrechung
Topologische Defekte
Atomic Friction and Symmetry-Breaking Transitions in Ion Coulomb Systems
oai:www.repo.uni-hannover.de:123456789/114182022-12-02T07:54:06Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
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Lee, Yongho
author
2021-09-16
A coupling between angular jitter of satellite and length readout, called tilt-to-length coupling, is one of the major noise sources in space-based laser interferometers such as LISA and GRACE Follow-On. With comprehensive knowledge of its characteristics and reduction, experimental investigations are an indispensable gateway to develop future space laser interferometers. A recurring difficulty in tilt-to-length coupling experiments is the motion errors of the actuators used to generate the tilting beam. This motion error then couples into the path length readout and cannot be distinguished from the tilt-to-length coupling under investigation.
Within this thesis, an optical testbed named advanced tilt actuator(ATA) was developed in order to provide a tilted beam and reduce the actuator’s parasitic longitudinal displacement, thereby enabling the characterisation of the tilt-to-length coupling. The actuator employed in the ATA can produce a motion in three degrees of freedom for yaw and pitch and a displacement and is used for tilting a beam needed in tilt-to-length experiments. The vertices of retroreflectors attached to the rear of the actuator are traced by dedicated interferometers, such that the actuator’s motion could be measured.
Although potential misalignments during the construction of the ATA endeavoured to be minimised through the devised alignment techniques, residual misalignment may degrade the advanced tilt actuator’s performance. Based on analytical and numerical analyses of the various misalignment effects, possible readouts errors that may appear in a real experiment were simulated. For counteracting the readout error due to misalignments, a calibration method enabling suppressing the longitudinal displacement readout error was established, and its validity was verified through numerical simulations.
As the purpose of the ATA, an optical breadboard for examining tilt-to-length coupling effects was constructed, aiming to experimentally demonstrate that the imaging system enables mitigating the tilt-to-length coupling. Prior to this experiment, suppressing the ATA’s longitudinal displacement readout error caused by various misalignments was performed through the calibration method. In the main experiment, we measured two path length readouts with and without the imaging system, applying the calibration enabling the suppression of linear and hysteresis error. The best experimental result with the imaging system showed tilt-to-length coupling of about 2μm/rad, which is a significantly better performance than the 25 μm/rad required for LISA. Additionally, the ATA’s angular readouts were compared with differential wavefront sensing signals measured on the optical breadboard, showing the measurement error in the order of a micro-radian within the rotation angle of ± 200 μrad.
Lee, Yongho: Development of an advanced tilt actuator for tilt-to-length coupling investigations. Hannover : Gottfried Wilhelm Leibniz Universität, Diss., 2021, XII, 181 S. DOI: https://doi.org/10.15488/11331
https://www.repo.uni-hannover.de/handle/123456789/11418
http://dx.doi.org/10.15488/11331
tilt-to-length coupling
LISA
actuator
space laser interferometer
tilt-to-length coupling
LISA
actuator
space laser interferometer
Development of an advanced tilt actuator for tilt-to-length coupling investigations
oai:www.repo.uni-hannover.de:123456789/114322022-12-02T07:59:27Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessstatus-type:publishedVersiondoc-type:DoctoralThesisddc:500
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Bartosch, Wolfgang
author
2021-10-04
Das Finden einer universellen Theorie der physikalischen Grundkräfte stellt
einen großen Teil der Anstrengungen der fundamentalen Physik im letzten Jahrzehnt
dar. Das Standartmodell der Teilchenphysik scheint mit Einsteins Relativitätstheorie
fundamental unvereinbar. Einen möglichen Ansatz, beide Theorien zu vereinigen
stellt die String Theorie da. Diese erlaubt allerdings neue kräftewelche zu einer Verletzung
derUniversalität des freien Falls führen können. DieUniversalität des freien falls
kann beispielsweise mittels lunar Laser ranging oder Torsionswaagen, aber auch mit
Atominterferometern getestet werden. Letztere sind unabhängig von Imperfektionen
mechanischer Fertigung der getestetenMassen und sie verwenden quantenmechanische
Testmassen. Die Sensitivität eines sochen Atominterferometers hängt stark von
der freien Entwicklungszeit eines kohärent geteilten atomaren Ensembles ab. Diese
wiederumkann vergrößertwerden, indem dieProbezumSchweben gebracht wird, indem
man den Testapparat vergrößert oder indem der Test inMikrogravitation durchgeführt
wird.
Diese Arbeit fokussiert sich auf den letzteren Ansatz und darauf wie man ein Elektroniksystem,
welches in der Lage ist einAtominterferometer autonom auf der Höhenforschungsraketenmission
MAIUS-2, ohne menschliches eingreifen zu steuern, bauen
kann.
DieHerausforderungenwelche die experimentelleUmgebung der Höhenforschungsrakete
an das Elektroniksystem stellt, werden in dieser Arbeit diskutiert. MiniaturisierteElektronikkomponenten,
welche für ein solchesExperiment nötig sind, wie Stromtreiber,
Mikrowellen quellenundrauscharmeSpannungsquellen,welche mit Laboraufbauten
konkurrieren können, werden im Rahmen dieser Arbeit vorgestellt.
Schlüsselparameter für das Design solcher Komponenten werden, einerseits von den
Anforderungen der Höhenforschungsrakte und andererseits denen des Experimentes
hergeleitet. Dies stellt immer eine Gradwanderung zwischen Miniaturisierung und
der best möglichen Performance desGeräts da, für diese hier ein Leitfaden geschaffen
wird. Diese Arbeit baut auf den Erfolgen der MAIUS-1 Mission auf, welche 2017 das
erste Rubidium 87 Bose-Einstein-Condensate (BEC) imWeltraum erzeugt hat, und erweitert
deren Möglichkeiten um eine zweite atomare Spezies: Kalium. Dabei ändern
sichMasse und Größe des Elektroniksystems und des experimentellen Aufbaus nicht
wesentlich. Das komplette hierfür entwickelte Elektroniksystem wird in dieser Arbeit
vorgestellt. Dabei wird verstärkt ein Augenmerk auf das System zur Mikrowellenevaporation
von Rubidium und Kalium gelegt. Ein weiter Fokus wird die Untersuchung
der Empfindlichkeit des Experimentes gegenüber Störungen in den Strömen desAtom
Chips sein um obere Schranken für die Rauschintensität zukünftiger Komponenten
festlegen zu können. Diese Arbeit legt den Grundstein für zukünftige Atominterferometer
Experimente imWeltraum, indem ein Anforderungskatalog für miniaturisierte,
präzisionsmesstechnische elektronische Systeme, solcher Apparate erstellt wird.
Bartosch, Wolfgang: The electronic and experimental setup of the MAIUS-2 and MAIUS-3 sounding rocket missions. Hannover : Gottfried Wilhelm Leibniz Universität, Diss., 2021, V, 148 S. DOI: https://doi.org/10.15488/11345
https://www.repo.uni-hannover.de/handle/123456789/11432
http://dx.doi.org/10.15488/11345
Atominterferometer
Elektronik
Mikrogravitation
The electronic and experimental setup of the MAIUS-2 and MAIUS-3 sounding rocket missions
oai:www.repo.uni-hannover.de:123456789/114492022-12-02T07:59:27Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
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Becker, Dennis
author
2021
Quantum sensors based on atom interferometry are precise measurement devices whose ultimate performance can be reached using Bose–Einstein condensates (BECs) in extended free fall. This thesis summarizes the endeavour of the QUANTUS and MAIUS collaborations to enable BECs for precision interferometry in space. The presented results have set the foundation for future space missions aiming at geodesy applications or tests of fundamental physics.
Becker, Dennis Vincent Daniel: Interferometry with Bose-Einstein condensates from ground to space. Hannover : Gottfried Wilhelm Leibniz Universität, Diss., 2021, i, 49 S. DOI: https://doi.org/10.15488/11362
https://www.repo.uni-hannover.de/handle/123456789/11449
http://dx.doi.org/10.15488/11362
atom interferometry
Bose-Einstein condensation
microgravity
space
Atominterferometrie
Bose-Einstein Kondensat
Schwerelosigkeit
Weltraum
Interferometry with Bose-Einstein condensates from ground to space
oai:www.repo.uni-hannover.de:123456789/115592022-12-02T07:47:02Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
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Fim, Dominika Barbara
author
2021
The primary frequency and time standard, defined via a transition frequency of caesium-133, is realized by microwave clocks reaching relative uncertainties in the 10−^16 level. This performance has been surpassed by state-of-the-art lattice clocks, with transition frequencies in the optical regime, leading to two orders of magnitude lower uncertainties. The key to this performance is the confinement in the Lamb-Dicke regime at the magic wavelength enabling a Doppler- and recoil-free spectroscopy with a first-order suppressed AC Stark shift. In atomic clocks, several effects contribute to the uncertainty of the transition frequency. Through continuous global characterization efforts, the individual uncertainty of these effects have been subsequently reduced. Yet one effect, namely the frequency shift induced by blackbody radiation has been identified as a dominant contribution which is difficult to overcome by technical means. In this regard, magnesium-24 excels as a species of choice as its blackbody radiation sensitivity is one order of magnitude lower than in the most frequently used atomic clock species. Furthermore, magnesium offers a relatively simple electronic structure which enables theoretical support through high-precision calculations. This thesis features the first characterization of a magnesium optical lattice clock operating at the magic wavelength. The characterization of the magnesium frequency standard presented in this thesis depends essentially on the resolution of the transition linewidth, which could be reduced from kHz range to 51(3) Hz in a complementing work. The realization of a transition linewidth with a quality factor of Q = 1.3 × 10^13 has contributed to an improved determination of the magic wavelength within this thesis to 468.4106(2) nm. Compared to earlier work, this represents an improvement of two orders of magnitude. Furthermore, the lower transition linewidth also allowed the first observation of the probe AC Stark shift and thus the first characterization of effects in the lattice that falsify the frequency of the trapped magnesium atoms. Overall, the relative uncertainty of the frequency-related effects influencing the clock transition could be determined to be 7.1 × 10^−15. The dominant contributions can be assigned to tunneling broadening and the lattice and probe AC Stark effects, induced by the probe and lattice light. All these effects can be traced back to technical limitations and are part of future work. Following the characterization, a first frequency comparison between the magnesium lattice clock against the primary frequency standard as well as the ytterbium ion clock at the PTB has been performed and thus a first realization of a lattice based frequency standard with magnesium atoms was demonstrated. The determined transition frequency of 655 058 646 681 864.1(5.3) Hz complies with former measurements. The primary frequency and time standard, defined via a transition frequency of caesium-133, is realized by microwave clocks reaching relative uncertainties in the 10^−16 level. This performance has been surpassed by state-of-the-art lattice clocks, with transition frequencies in the optical regime, leading to two orders of magnitude lower uncertainties. The key to this performance is the confinement in the Lamb-Dicke regime at the magic wavelength enabling a Doppler- and recoil-free spectroscopy with a first-order suppressed AC Stark shift. In atomic clocks, several effects contribute to the uncertainty of the transition frequency. Through continuous global characterization efforts, the individual uncertainty of these effects have been subsequently reduced. Yet one effect, namely the frequency shift induced by blackbody radiation has been identified as a dominant contribution which is difficult to overcome by technical means. In this regard, magnesium-24 excels as a species of choice as its blackbody radiation sensitivity is one order of magnitude lower than in the most frequently used atomic clock species. Furthermore, magnesium offers a relatively simple electronic structure which enables theoretical support through high-precision calculations. This thesis features the first characterization of a magnesium optical lattice clock operating at the magic wavelength. The characterization of the magnesium frequency standard presented in this thesis depends essentially on the resolution of the transition linewidth, which could be reduced from kHz range to 51(3) Hz in a complementing work. The realization of a transition linewidth with a quality factor of Q = 1.3 × 10^13 has contributed to an improved determination of the magic wavelength within this thesis to 468.4106(2) nm. Compared to earlier work, this represents an improvement of two orders of magnitude. Furthermore, the lower transition linewidth also allowed the first observation of the probe AC Stark shift and thus the first characterization of effects in the lattice that falsify the frequency of the trapped magnesium atoms. Overall, the relative uncertainty of the frequency-related effects influencing the clock transition could be determined to be 7.1 × 10^−15. The dominant contributions can be assigned to tunneling broadening and the lattice and probe AC Stark effects, induced by the probe and lattice light. All these effects can be traced back to technical limitations and are part of future work. Following the characterization, a first frequency comparison between the magnesium lattice clock against the primary frequency standard as well as the ytterbium ion clock at the PTB has been performed and thus a first realization of a lattice based frequency standard with magnesium atoms was demonstrated. The determined transition frequency of 655 058 646 681 864.1(5.3) Hz complies with former measurements.
Fim, Dominika Barbara: First optical lattice frequency standard based on 24Mg atoms. Hannover : Gottfried Wilhelm Leibniz Universität, Diss., 2021, i, 96 S. DOI: https://doi.org/10.15488/11470
https://www.repo.uni-hannover.de/handle/123456789/11559
http://dx.doi.org/10.15488/11470
optical frequency standard
precision spectroscopy
frequency comparison
Optischer Frequenzstandard
hoch präzise Spektroskopie
Frequenzvergleich
First optical lattice frequency standard based on 24Mg atoms
oai:www.repo.uni-hannover.de:123456789/116542022-12-02T07:47:02Zcom_123456789_11com_123456789_15com_123456789_2961col_123456789_18col_123456789_2962col_123456789_14doc-type:Textopen_accessstatus-type:publishedVersiondoc-type:DoctoralThesisddc:500
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Setyawati, Yoshinta Eka
author
2021-09-29
The first direct gravitational wave detection by LIGO and Virgo in 2015 marked the beginning of the gravitational wave astronomy era. Gravitational waves are an excellent tool to prove general relativity and unveil compact objects' dynamics in the universe. Over the years, we observe more signals from coalescing black hole binaries.
Signals from the detectors are filtered through numerous waveform templates coming from theoretical predictions. Some models are more accurate but slow, and the others are less accurate but fast. We face ever-increasing demands for accuracy, speed, and parameter coverage of waveform models with more detections. Thus, we investigate strategies to speed up waveform generation without losing much accuracy for future signal analysis.
In this dissertation, we present our approach as follows:
1. developing a method to dynamically tune less accurate (but fast) models with a more accurate (but slow) models through an iterative dimensionality reduction technique,
2. investigating the performance of regression methods, including machine learning for higher dimensions,
3. adding eccentricity to quasicircular analytical models through fitting technique.
We analyze our results' faithfulness and prospects to speed up waveform generation. Our methods can readily be applied to reduce the complexity and time of building a new waveform model. Additionally, we build a python package pyrex to carry out the quasicircular turned eccentric computation. This study is crucial for the development of models which include more parameters.
Setyawati, Yoshinta Eka: Accurate and rapid gravitational waveform models for binary black hole coalescences. Hannover : Gottfried Wilhelm Leibniz Universität, Diss., 2021, x, 166 S. DOI: https://doi.org/10.15488/11563
https://www.repo.uni-hannover.de/handle/123456789/11654
http://dx.doi.org/10.15488/11563
Gravitational wave
Waveform modeling
Machine learning
Binary black-hole
Gravitationswelle
Wellenformmodellierung
maschinelles Lernen
binäres schwarzes Loch
Accurate and rapid gravitational waveform models for binary black hole coalescences
oai:www.repo.uni-hannover.de:123456789/116552022-12-02T07:47:02Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
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Borchert, Matthias Joachim
author
2021
This thesis describes high precision measurements on the fundamental properties of the antiproton, namely the charge-to-mass ratio and the magnetic moment. This work is embedded in the experimental work of the BASE collaboration (Baryon Antibaryon Symmetry Experiment). BASE operates a sophisticated cryogenic Multi-Penning trap system in the Antiproton Decelerator facility at CERN. One main result of this thesis are significant technical improvements of the apparatus, which reduced the limitation of shot-to-shot cyclotron frequency scatter by a factor of more than five compared to earlier work.
With this improved apparatus, a measurement campaign on the antiproton-to-proton charge-to-mass ratio with a statistical uncertainty of 20×10−12 and an overall uncertainty of about 35 × 10−12 was conducted. This campaign was part of a series of charge-to-mass ratio measurements on the antiproton with the overall goal to significantly improve the previous best measurement conducted by BASE in 2014, which yielded a fractional uncertainty of 69×10−12. In this thesis, also the first dedicated heating rate measurement in a cryogenic Penning trap experiment is described. Here, the lowest heating rates ever reported for an ion trap were observed. As part of this thesis, phase sensitive methods for measuring the cyclotron frequency of a single trapped ion were implemented in the BASE experiment. These methods allowed to measure the cyclotron frequency with a shot-to-shot scatter improved by a factor of five compared to methods used in previous experiments. The significant improvements in cyclotron frequency scatter open up the possibility to measure the antiproton magnetic moment and the antiproton charge-to-mass ratio with much increased precision, and thereby enable more stringent tests of the fundamental CPT symmetry by direct comparisons of matter/antimatter conjugates.
Borchert, Matthias Joachim: Challenging the Standard Model by high precision comparisons of the fundamental properties of antiprotons and protons. Hannover : Gottfried Wilhelm Leibniz Universität, Diss., 2021, xiv, 246 S. DOI: https://doi.org/10.15488/11564
https://www.repo.uni-hannover.de/handle/123456789/11655
http://dx.doi.org/10.15488/11564
Penning trap
Antiproton
Charge-to-mass ratio
Penningfalle
Antiproton
Masse-zu-Ladung-Verhältnis
Challenging the Standard Model by high precision comparisons of the fundamental properties of antiprotons and protons
oai:www.repo.uni-hannover.de:123456789/117212022-12-02T07:47:02Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
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Li, Wei-Han
author
2021
This Thesis is devoted to the study of particle mobility in polar lattice gases, that
is, systems of particles with a large magnetic or electric dipole moment loaded in a deep optical lattice, which may move between sites via hopping. Our detailed analysis of different scenarios shows that inter-site dipole-dipole interactions largely handicap particle motion, resulting in a lattice dynamics that differs qualitatively, and not only quantitatively, to that expected both for non-dipolar gases, and for systems with exclusively nearest-neighbor interactions. We first discuss how the formation of dynamically-bound nearest-neighbor dimers for large enough dipolar interactions, results in an anomalously slow dynamics and quasi-localization due to the formation of dimer clusters. Moreover, we show that even modest inter-site interactions result in the formation of self-bound lattice droplets. We then extend the discussion to general states, placing the discussion in the frame of current studies on disorder-free localization, dynamical constraints and Hilbert-space fragmentation. We are particularly concerned with the difference between a polar lattice gas and a system with purely nearest-neighbor interactions. In the latter, strong-enough inter-site interactions lead to fragmentation, but resonant dynamics remains possible within a fragment, precluding disorder-free spatial localization. In contrast, in a polar gas, the presence of the dipolar tail shatters the Hilbert space, and in addition disrupts the resonant mechanism characteristic of the nearest-neighbor model. As a result, we show that the particle dynamics is dramatically slowed-down, and eventually localized in absence of any disorder, for interaction strengths within reach of experiments. Furthermore, although most of the results of this Thesis concern one-dimensional systems, most of the results can be extrapolated to higher dimensions. Moreover, we show that the dynamics in two-dimensional polar lattice gases presents peculiar features, due to the fact that dynamically-bound dimers experience a lattice different than that of individual particles. In particular, dimers in triangular lattices move in an effective kagome lattice, presenting an effective flat band. We show that the presence of flat-band dimers results in a peculiar multi-scaled quantum walk dynamics, and in a long-lived memory of initial conditions in absence of any disorder. The results in this Thesis open exciting perspectives in what concerns particle dynamics and disorder-free localization in on-going and future experiments with magnetic atoms and polar molecules in optical lattices. Furthermore, our findings may be easily extrapolated to other power-law interactions, as those realizable using trapped ions.
Li, Wei-Han: Interaction-induced localization and constrained dynamics in polar lattice gases. Hannover : Gottfried Wilhelm Leibniz Universität, Diss., 2021, vii, 122 S. DOI: https://doi.org/10.15488/11628
https://www.repo.uni-hannover.de/handle/123456789/11721
http://dx.doi.org/10.15488/11628
Localization
Quantun Statistics
Polar lattice gases
Lokalisierung
Quantenstatisti
Polare Gittergase
Interaction-induced localization and constrained dynamics in polar lattice gases
oai:www.repo.uni-hannover.de:123456789/117152022-12-02T07:47:02Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
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Herbers, Sofia
author
2021
In this work, a transportable ultra-stable laser system based on a Fabry-Pérot cavity with crystalline aluminium gallium arsenide (Al₀․₉₂Ga₀․₀₈As) / gallium arsenide (GaAs) mirror coatings, fused silica glass mirror substrates and a 20 cm-long ultra low expansion glass spacer was designed and built to serve as a clock laser for a ⁸⁷Strontium (Sr) lattice clock. The laser system uses an external-cavity diode laser, which is stabilized to a resonance frequency of the Fabry-Pérot cavity using the Pound-Drever-Hall method. This reduces the laser's fractional frequency instability down to the cavity's fractional length instability. Due to the high absorbance of Al₀․₉₂Ga₀․₀₈As/GaAs mirror coatings for visible light, the laser is operated at a wavelength of 1397 nm, which is twice the transition wavelength of a ⁸⁷Sr lattice clock. The laser system therefore includes frequency doubling and light distribution for operation of a ⁸⁷Sr lattice clock. The fundamental limit of the cavity's fractional length instability and thus the laser's fractional frequency instability is determined by the thermal noise floor resulting from Brownian, thermoelastic and thermorefractive noise of the cavity components. The calculated thermal noise floor limit given as modified Allan deviation of the fractional frequency instability mod σᵧ is below 1 · 10⁻¹⁶. Besides the thermal noise, technical noise caused by seismic noise, residual amplitude modulation, laser power, pressure, optical path length and temperature fluctuations affects the laser's fractional frequency instability. The single contributions of the technical noise were investigated and their impact on the laser's fractional frequency instability were suppressed below the thermal noise floor for averaging times around one second using passive or active stabilization. The laser system achieves an instability as low as mod σᵧ = 1.6 · 10⁻¹⁶, which is already a factor 1.3 lower than the theoretically possible instability of mod σᵧ = 2 · 10⁻¹⁶ for the same resonator with tantalum pentoxide (Ta2O5) / fused silica (SiO2) mirrors. This is the lowest fractional frequency instability among published transportable laser systems. Depending on the averaging time of interest, the fractional frequency instability has been reduced by a factor of up to seven compared to Physikalisch-Technische Bundesanstalt (PTB)'s current transportable laser system, which had the lowest fractional frequency instability until now. This reduced instability allows a reduction of the Dick effect limit by roughly a factor of four for interrogation times below 0.5 s, which would reduce the clock's instability limit significantly.
Herbers, Sofia: Transportable ultra-stable laser system with an instability down to 10⁻¹⁶. Hannover : Gottfried Wilhelm Leibniz Universität, Diss., 2021, iv, 94 S., v-xix, DOI: https://doi.org/10.15488/11624
https://www.repo.uni-hannover.de/handle/123456789/11715
http://dx.doi.org/10.15488/11624
ultra-stable optical cavitiy
ultra-stable optical resonator
transportable clock laser system
transportable interrogation laser system
crystalline Al₀․₉₂Ga₀․₀₈As/GaAs mirror coatings
ultrastabile optische Resonatoren
transportabler Uhrenlaser
kristalline Al₀․₉₂Ga₀․₀₈As/GaAs Spiegelbeschichtung
Transportable ultra-stable laser system with an instability down to 10⁻¹⁶
oai:www.repo.uni-hannover.de:123456789/120242022-12-02T07:54:05Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
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Schwarz, Roman
author
2022
Optical clocks have moved to the forefront of frequency metrology. Their outstanding
performances enable the exploration of new fields of research such as the search for dark
matter and dark energy [1, 2], temporal drifts of the fine structure constant alpha [3, 5], violations
of the Einstein equivalence principle (EEP) [6], and new applications such as
chronometric leveling [7]. State-of-the-art optical clocks outperform the current realization
of the SI-unit "Second" by the 133cesium fountain clocks, by two orders magnitude
or more in instability and accuracy which triggers a discussion on a re-definition of the
second. In 2016 the Consultative Committee for Time and Frequency (CCTF) of the
International Bureau of Weights and Measures (BIPM) released a roadmap towards a redefinition of the SI second. One of the requests is the characterization of the systematic
uncertainty of at least three independent clocks at the level of 10^-18. In this work, PTB's
new cryogenic strontium lattice clock, Sr3, operating on the 1S0 - 3P0 clock transition
in neutral 87Sr is described. Its systematic uncertainty has is evaluated to 2.7 x 10^-18 in
fractional frequency units. This represents an improvement of more than a factor of 5
compared to its predecessor system Sr1 [8]. In Sr1 the dominant contribution of frequency
uncertainty was about 1.4 x 10^-17 from the uncertainty of the black-body radiation (BBR)
frequency shift. It arose from temperature gradients across the in-vacuum magnetic field
coils that are placed close to the atoms. Reducing the gradients was not possible which ultimately
limited the systems achievable systematic uncertainty. Sr3 features an in-vacuum
dual-layer environment, the cryostat, that provides a very homogeneous temperature distribution
for the atoms. This translates to a lower BBR frequency shift uncertainty as
Sr1 at room temperature operation. The corresponding total systematic uncertainty for
room temperature operation was evaluated to about 3.5 x 10^-18. Furthermore Sr3 features
a closed-cycle pulse tube cooler that allows to operate the cryostat at any temperature
ranging from room temperature to about 80K to further reduce the BBR frequency shift
and uncertainty where the systematic uncertainty reaches the value of 2.7 x 10^-18 as mentioned
above.
Sr3 also features an arrangement of electrodes that allow the characterization of the
dc-Stark frequency shift in three dimensional space. In this work the characterization of
the electrode arrangement is described and the determination of the dc Stark shift. In Sr1
the this capability was limited to one direction that was pointing along the quantization
magnetic field axis.
During clock operation of Sr1, several high-accuracy comparisons to other atomic
clocks have been performed. This includes many absolute frequency measurements yielding
in a new record uncertainty in the transition frequency. An absolute frequency of Sr1
of f(Sr1) = 429 228 004 229 873.00(7)Hz [8] was measured that is in agreement withe the one
measured of Sr3 of f(Sr3) = 429 228 004 229 872:94(19)Hz. The statistical uncertainty the measurements was significantly improved by using a H-Maser as a
flywheel oscillator toeither extend the dataset or to bridge downtimes of the Sr-clocks [9].
Optical frequency ratio measurements between either of the two strontium clocks and
the on-campus 171Yb+ single-ion clock have been carried out [10] for direct determination
of their frequency ratio beyond the limitation of the primary frequency standards represented
by Cs fountain clocks. The ratio measurements involving Sr1 span over a period of
more than seven years and more than half a year with Sr3. The measurements have also
revealed that the frequency ratio of the clocks, are reproducible within their uncertainties
on short time scales but exhibits unexpected large scatter in the long term. The observed
variations are on the order of several 10^-17 which is beyond any of the clocks reported
systematic uncertainty. Despite an excessive search no uncontrolled frequency shifts were
found.
In the near future the in-vacuum cryostat is supposed to be updated with rotatable
shutters. They will allow to minimize the BBR shift uncertainty during cryogenic operation.
Prospectively a BBR shift uncertainty at the low 10^-19 level can be expected which
paves the way for the system to reach a total systematic uncertainty of below 1 x 10^-18.
Schwarz, Roman: A cryogenic Strontium lattice clock. Hannover : Gottfried Wilhelm Leibniz Universität, Diss., 2022, x, 166 S. DOI: https://doi.org/10.15488/11929
https://www.repo.uni-hannover.de/handle/123456789/12024
http://dx.doi.org/10.15488/11929
Strontium lattice clock
Frequency standard
Blackbody radiation frequency shift
Strontium Gitteruhr
Frequenzstandard
Schwarzkörperstrahlung
A cryogenic Strontium lattice clock
oai:www.repo.uni-hannover.de:123456789/120272022-12-02T07:59:27Zcom_123456789_11com_123456789_2961col_123456789_2962col_123456789_14doc-type:Textopen_accessddc:530status-type:publishedVersiondoc-type:DoctoralThesis
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Krause, Florian
author
2022
In this thesis a new practical realization of the meter at a wavelength of 633 nm with a diode laser stabilized on iodine is investigated, with the aim of replacing the old technology of He-Ne lasers with more effective diode lasers. The frequency of an external cavity diode laser is stabilized to the Doppler-free hyperfine transitions of iodine (127^I_2) using noise-immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) technique. The performance of the system was investigated in comparison to a primary Cs atomic clock via a frequency comb. The diode laser is stabilized by using the NICE-OHMS method to a 14 cm external cavity containing a 10 cm long iodine cell. It achieves a short time frequency instability of 1.4 · 10^(−12) for an averaging time of 1 s, an improvement by a factor of four compared to an iodine stabilized He-Ne laser, which is widely used as practical realization of the meter. The uncertainty of the NICE-OHMS system is 28 kHz. Practical experiments as well as simulations are performed to identify effects that influence the frequency of the laser. To replace two-mode or Zeeman-stabilized He-Ne lasers, also a shoe box size diode laser system stabilized to Doppler broadened iodine lines is investigated. This system, which uses a 3 cm iodine cell, covers a frequency range of several 100 GHz, and achieves an output power of 5 mW. It automatically stabilizes to iodine lines and has a frequency instability of 2·10^(−10) for averaging times of 1 s, which is adequate for industrial interferometry
applications.
Krause, Florian: Iodine stabilized diode laser using Noise-Immune Cavity-Enhanced Optical Heterodyne Molecular Spectroscopy for the practical realisation of the meter at 633 nm. Hannover : Gottfried Wilhelm Leibniz Universität, Diss., 2022, vi, 135 S., DOI: https://doi.org/10.15488/11932
https://www.repo.uni-hannover.de/handle/123456789/12027
http://dx.doi.org/10.15488/11932
diode laser
optical cavity
Pound-Drever-Hall
NICE-OHMS
fm-spectroscopy
saturation spectroscopy
iodine
SI-unit meter
Diodenlaser
optischer Resonator
Pound-Drever-Hall
NICE-OHMS
FM-Spektroskopie
Sättigungs Spektroskopie
Iod
SI-Einheit Meter
Iodine stabilized diode laser using Noise-Immune Cavity-Enhanced Optical Heterodyne Molecular Spectroscopy for the practical realisation of the meter at 633 nm
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