Atom interferometry with ultracold atoms for inertial sensing

Abstract

In light pulse atom interferometry wave packets are spatially separated and recombined in a coherent manner by interacting with laser pulses. Typically, two photon transitions are used to perform Rabi oscillations between two internal or/and external states to construct atom-optical elements, like beam splitters or mirrors. The phase difference accumulated between two atomictrajectories can be used to measure quantities such as accelerations or rotations. The velocity distribution and size of the employed atomic sources can significantly limit the efficiency of the atom-light interactions and thus the performance of the interferometer. To overcome this limitation, ensembles with momentum distributions far below the recoil of a photon are used, such as collimated Bose-Einstein condensates (BEC).

Exploiting the properties of a BEC opens up a wide range of possibilities for new techniques and concepts, especially for increasing the sensitivity of measurements performed in small volumes. This work presents some of these novelties. The technique of an innovative (re-)launch mechanism helps to effectively increase the available interferometry time in compact gravimeter setups. A symmetric large momentum transfer in the form of a twin-lattice enables the enclosure of large space-time areas suitable for rotation measurements with high sensitivities. The exploitation of a BEC in combination with momentum transfer by double Bragg diffraction contributed to the development of a new concept. Using a single BEC, it is possible to create two simultaneous interferometers, which are employed to differentiate between rotations and accelerations. Its symmetry allows this geometry to be extended to form the basis of a six-axis quantum inertial measurement unit. Last but not least, the (re-)launch in combination with the symmetric splitting also provides the basis for a multi-loop atom interferometer. With this concept, an area can be enclosed that offers unique scalability for rotational sensors. Each atom interferometer is affected by the quality of its interrogating light fields. Therefore specific detrimental effects are pointed out in this work and possible mitigation strategies are presented subsequently. One way to reduce the susceptibility of light beams to distortions at apertures is to change their profile from the commonly used Gaussian profile to a more locally limited intensity distribution. For this purpose, the application of flat-top beam profiles is investigated. This brings the added benefit of a uniform power distribution, which helps to increase the beam area in which the ensemble of atoms can be manipulated with the same properties. Imperfections can also lead to position-dependent dipole forces that have a parasitic effect on the output of an interferometer. Especially for large momentum transfer techniques this has proven to be a limitation which can necessitate a compensation mechanism. To this end, a laser system is constructed that achieves the required high laser powers and includes additional frequency components.

Many of the interferometry methods and concepts introduced are well suited for compact or transportable systems. For this purpose, a laser system based on telecommunication fiber components is presented, which represents an all-in-one solution for the generation, preparation and subsequent beam splitting of ultracold atoms. Inspired by all of the above, the future vision of a quantum sensor for inertial navigation applications is discussed.