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Ultracold Bose gases in random potentials: collective excitations and localization effects

Pierre Lugan 1
1 laboratoire Charles Fabry de l'Institut d'Optique / Optique atomique
LCFIO - Laboratoire Charles Fabry de l'Institut d'Optique
Abstract : In this thesis, we theoretically investigate the localization properties of weakly-interacting Bose gases in the presence of one-dimensional disorder. We focus on three aspects of those disordered systems. First, we study the case of a non-interacting gas. According to general results, all single-particle states are localized in one dimension. We show that for certain classes of correlated disorder, the dependence of the localization length of the atoms on their energy undergoes sharp crossovers for weak disorder. These findings allow for the interpretation of recent experiments beyond previous analyses. Then, we examine the ground state of an interacting gas, and establish a diagram of the quantum states as a function of the strength of disorder and interactions. We analyze the density modulations imposed on the gas by the disorder, in order to describe the crossover from the regime of delocalized Bose-Einstein condensate to the regime of fragmented condensate. For the regime of very weak interactions, we develop a microscopic description of the system on the basis of the eigenstates of the single-particle Hamiltonian. These results contribute to characterizing the Bose-glass phase at weak interactions, which has yet to be explored thoroughly. Finally, we study the localization of the elementary excitations of the Bose gas in the (quasi-) condensate regime. We show that the suppressed localization of the excitations of lowest energy is due to an efficient screening by the (quasi-) condensate of the long-wavelength variations of the external potential.
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Contributor : Pierre Lugan <>
Submitted on : Wednesday, March 31, 2010 - 7:41:28 PM
Last modification on : Wednesday, September 16, 2020 - 5:38:09 PM
Long-term archiving on: : Wednesday, September 8, 2010 - 8:21:16 PM

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  • HAL Id : tel-00468888, version 1

Citation

Pierre Lugan. Ultracold Bose gases in random potentials: collective excitations and localization effects. Atomic Physics [physics.atom-ph]. Ecole Polytechnique X, 2010. English. ⟨tel-00468888⟩

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