Gaz bidimensionnels désordonnés : diffusion et transition superfluide

Baptiste Allard 1
1 Laboratoire Charles Fabry / Optique atomique
LCF - Laboratoire Charles Fabry
Abstract : This manuscript shows an experimental study of a disordered ultra-cold 87Rb gas confined in two dimensions.In the first part, we set up the experimental tools used to manipulate the confined gases. After a state of the art in ultracold 2D Bose gases, we describe our disorder-free experiment from which, by a comparison with quantum Monte-Carlo calculations and thanks to an accurate time-of-flight thermometry, we are able to quantify the emergence of coherence around the Berezinskii-Kosterlitz-Thouless superfluid phase transition. The second part is devoted to the effect of a micrometer-range optically generated disordered potential on the transport and coherence properties of the interacting 2D gas. This part follows the experimental road from the regime of classical transport, in which we have measured the energy dependence of the classical diffusion coefficient, to the regime of quantum transport we have just reached thanks to a last cooling step. On the road between those two regimes, we observe a shift towards lower entropy of the emergence of coherence close to the BKT transition as a response of an adiabatic addition of a moderate amount of disorder. It is strongly suppressed for an amount of disorder of the order of the cloud temperature. This work is a first step to an experimental study of the quantum transition to the Bose-Glass phase involving disorder and interaction.
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Baptiste Allard. Gaz bidimensionnels désordonnés : diffusion et transition superfluide. Autre [cond-mat.other]. Université Paris Sud - Paris XI, 2012. Français. ⟨NNT : 2012PA112223⟩. ⟨tel-00777687⟩

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