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Exploration de la physique à deux dimensions avec des gaz de Bose dans des potentiels à fond plat : ordre en phase et symétrie dynamique

Abstract : The thermodynamic properties and the dynamical behaviour of two-dimensional systems differ notably from the ones in three dimensions. This work presents experiments performed with ultracold clouds of uniform weakly interacting bosons confined in two dimensions of space. These experiments explore some specific features of the thermodynamics and the out-of equilibrium dynamics of two-dimensional systems. Working with ultracold atoms provides the experimentalist with a rich toolbox: geometry, temperature and internal state of the system are well controlled, and various methods to investigate their properties are available. In particular we work with uniform Boses gases in highly tunable geometries. I describe the set-up and our experimental toolbox in a first part. In a second part I present experiments to investigate the Berezinskii-Kosterlitz-Thouless transition of a two-dimensional Bose gas. It is a topological phase transition for which the system displays a quasi-long range order below the critical temperature. We have developed two experimental schemes to probe this quasi-long range order. In a third and final part I explain the symmetries that underlie the dynamics of a cloud near zero temperature in a harmonic potential. These symmetries are the hidden symmetries of the two-dimensional non-linear Schrödinger equation, which describes many other physical systems. We could probe these symmetries experimentally, and we also observed initial shapes whose evolution is periodic in a harmonic potential in the presence of a non-linearity. They could constitute new breathers of this non-linear equation.
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https://tel.archives-ouvertes.fr/tel-03116129
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Submitted on : Wednesday, January 20, 2021 - 10:02:07 AM
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  • HAL Id : tel-03116129, version 1

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Raphaël Saint-Jalm. Exploration de la physique à deux dimensions avec des gaz de Bose dans des potentiels à fond plat : ordre en phase et symétrie dynamique. Physique Quantique [quant-ph]. Université Paris sciences et lettres, 2019. Français. ⟨NNT : 2019PSLEE058⟩. ⟨tel-03116129⟩

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