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Propriétés d'équilibre et de transport de gaz de Bose bidimensionnels en présence de désordre

Thomas Plisson 1
1 Laboratoire Charles Fabry / Optique atomique
LCF - Laboratoire Charles Fabry
Abstract : In this thesis, we study the influence of disorder on the transport and equilibrium properties of two-dimensional (2D) Bose gases in the regime of quantum degeneracy. The systems we study are ultra-cold clouds of Rubidium 87, cooled and trapped by optical means, confined in 2D between two light sheets. The disordered potential is generated by laser speckles. The first experiment we describe studies the coherence properties of an interacting gas in the vicinity of the superfluid transition, called Berezinskii-Kosterlitz-Thouless transition. We quantitatively study the behavior of the momentum distribution of the gas through time-of-flight measurements. Our results are in agreement with Quantum Monte-Carlo simulation. In the presence of disorder, we observe that the growth of coherence is shifted to lower entropies. This result is a first step to the detailed study of the combined effects of interactions and disorder for 2D Bose gases. Our second experiment is a study of the transport properties of a 2D gas expanding in disorder. We first analyse in details the classical diffusion regime. We observe the characteristic decay of the central density with time and measure the diffusion coefficients depending on energy. The experimental results are in agreement with a specially developed classical numerical simulation. We then describe the experimental progress to reach the regime of quantum diffusion and Anderson localisation, together with a numerical simulation, with which we investigate experimental signatures of weak and strong localisation.
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Submitted on : Wednesday, November 28, 2012 - 11:04:47 PM
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Thomas Plisson. Propriétés d'équilibre et de transport de gaz de Bose bidimensionnels en présence de désordre. Gaz Quantiques [cond-mat.quant-gas]. Ecole Polytechnique X, 2012. Français. ⟨pastel-00758575⟩

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