Soutenance de thèse de Guillaume THEMEZE

Soutenance de thèse de Guillaume THEMEZE, doctorant dans le groupe Gaz quantiques du Laboratoire Charles Fabry, le mardi 4 novembre à 14h00 dans l'Auditorium de l'Institut d'Optique Graduate School à Palaiseau, sur le thème : "Study of the out-of-equilibrium dynamics of one-dimensional Bose gases."

Abstract: "This thesis focuses on the experimental and theoretical study of one-dimensional quantum gases out of equilibrium, using ultracold rubidium-87 atoms trapped on an atom chip. This setup provides strong transverse confinement and precise longitudinal control, enabling the exploration of exotic situations such as the quantum analogue of Newton’s cradle.

In this regime, interactions are described by the integrable Lieb–Liniger model, solvable by the Bethe Ansatz method. Such systems do not thermalize according to the standard Gibbs ensemble, but rather via the Generalized Gibbs Ensemble (GGE). I initiated theoretical work on the calculation of observable fluctuations, necessary to test this description, although no corresponding experimental measurements were carried out.

Generalized Hydrodynamics (GHD) complements the GGE by describing the large-scale dynamics of integrable gases. In this framework, we investigated dynamics of the “quantum Riemann problem” type and developed an experimental device based on a Digital Micromirror Device (DMD) to shape potentials and locally probe the rapidity distribution, paving the way for controlled out-of-equilibrium configurations.

Finally, we explored alternatives to chip-based magnetic confinement, in particular implementing an optical dipole trap that provides increased flexibility in engineering longitudinal potentials.

In summary, this thesis combines experimental and theoretical advances in the preparation and manipulation of integrable bosonic gases, the development of novel local probing tools, and the connection to modern theoretical frameworks for relaxation and dynamics (GGE and GHD)."