Time-averaged optical potentials for creating and shaping Bose-Einstein condensates

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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

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The precision of atom interferometers, targeted for example in the Hannover VeryLong Baseline Atom Interferometer (VLBAI) facility, imposes stringent requirementsin several respects. They concern the control of center-of-mass motion and expansionof 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 wavefrontaberrations, can be lowered. These requirements can be matched by employingultracold quantum gases or even quantum degenerate gases. A promising methodto create those ensembles is evaporative cooling in a spatially modulated opticaldipole trap. Here, the utilization of time-averaged potentials enables the fast creationof ultracold atomic ensembles with large number of atoms. Both, the highernumber of atoms and the increased repetition rate, enhance the performance of theinterferometer 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 thematter-waves by techniques such as matter-wave lensing or Delta-Kick collimationis also feasible due to the dynamic control of the trapping potential.In this thesis the implementation and application of dynamic time-averaged opticalpotentials created via center position modulation of dipole trap beams isdemonstrated. By evaporative cooling in these potentials, 1.9(0.4) x 10^5 condensedatoms with an expansion temperature of 29.2(1.3) nK were achieved after 3 s ofevaporation. Up to 4.2(0.1) x 10^5 condensed atoms could be observed with slowerevaporation of 5 s. Subsequent matter-wave lensing is carried out yielding expansionrates as low as 553(49) μms^-1 resulting in an effective temperature of 3.2(0.6) nK intwo dimensions. This lens can be applied at any stage of evaporative cooling, thusshort-cutting the generation of ultracold effective temperatures. In this thesis thelimitations of optical matter-wave lensing in the current setup are revealed andways to improve the performance are discussed.The fast generation of ultracold atomic ensembles will enhance the performance ofthe dual-species atom interferometer, which represents the experiment apparatusfor this thesis and strives for a test of the Universality of Free Fall with an uncertaintyon the order of 10^-9. The results of this thesis were used to test numericalsimulations which were utilized to show the perspective of generating up to 10^6collimated condensed atoms within 1 s of cycle time in the rubidium source systemof Hannover’s VLBAI.
License of this version: CC BY 3.0 DE
Document Type: doctoralThesis
Publishing status: publishedVersion
Issue Date: 2020
Appears in Collections:Dissertationen

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    other countries 37 10.85%

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