Coherent transport of ultracold atoms in disordered potentials : Manipulation of time-reversal symmetry in weak localization experiments

Kilian Muller 1
1 Laboratoire Charles Fabry / Optique atomique
LCF - Laboratoire Charles Fabry
Abstract : In this manuscript the coherence effects of wave propagation in disordered potentials is studied. Our experiment uses ultracold atoms as a probe, a system allowing for a very good control over parameters such as the dimensionality, interactions, initial velocity of the atoms, and the potential landscape. Exploiting this flexibility we were able to perform experiments in the strongly and the weakly localized regime. In the former the 3D expansion of a BEC was monitored in real space, resulting in the observation of 3D Anderson localization with a maximum localized fraction of about 20%. In the latter the atoms were launched into a quasi-2D disorder with a well defined initial velocity. Monitoring the momentum space distribution the mean scattering time and the transport time can be directly measured, and coherent backscattering (CBS) is clearly visible as a peak in the backwards direction. In a first set of experiments the evolution of the CBS amplitude and width were recorded and found to be in good agreement with theory. Microscopically, CBS stems from the constructive interference of time-reversed multiply scattered paths. In a second set of CBS experiments we manipulated the time-reversal symmetry (TRS) of the wave propagation. A surgical dephasing was introduced via a shortly pulsed gradient field, which brakes TRS and suppresses CBS except for a brief moment, when a revival of CBS is observed. This novel effect showcases explicitly the role of coherence and TRS in Coherent Backscattering and weak localization.
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Kilian Muller. Coherent transport of ultracold atoms in disordered potentials : Manipulation of time-reversal symmetry in weak localization experiments. Optics [physics.optics]. Institut d’Optique Graduate School, 2014. English. ⟨NNT : 2014IOTA0013⟩. ⟨tel-01127067⟩

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