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Exploring two-dimensional physics with Bose gases in box potentials: phase ordering and dynamical symmetry

Abstract : The physics of two-dimensional systems is strongly different from the physics in three dimensions: their thermodynamical properties and their dynamical behaviour can differ in low dimensions. This work presents experiments performed with ultracold clouds of uniform weakly interacting bosons confined in two dimensions of space. These experiments explore some particularities of the thermodynamics and the dynamics of two-dimensional systems. Working with ultracold atoms provides the experimentalist with a rich toolbox: the geometry, the temperature, the internal state of the system is very well controlled, and the methods to investigate its properties are manifold. 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 that displays quasi-long range order. We have developed a first experimental scheme to probe this quasi-long range order, which was not as reliable as expected. We then have found a second experimental procedure that provides more accurate results. 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 system. 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-02464649
Contributor : Raphaël Saint-Jalm <>
Submitted on : Monday, February 3, 2020 - 1:11:42 PM
Last modification on : Tuesday, September 22, 2020 - 3:45:54 AM
Long-term archiving on: : Monday, May 4, 2020 - 2:15:44 PM

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  • HAL Id : tel-02464649, version 1

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Raphaël Saint-Jalm. Exploring two-dimensional physics with Bose gases in box potentials: phase ordering and dynamical symmetry. Quantum Physics [quant-ph]. Université Paris Sciences et Lettres, 2019. English. ⟨tel-02464649⟩

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