Description du sujet de thèse

The goal of this thesis project is to study the dynamics and thermodynamics of out-of-equilibrium quantum gases. In the frame of ANR project RELAQS, a quantum gas of rubidium confined in a two-dimensional geometry will be prepared strongly out of equilibrium. The PhD candidate will first study the best excitation protocol to prepare in a controllable and reproducible way the excited sample. They will then look for the presence of non-thermal fixed points in its subsequent evolution towards equilibrium, by looking for universal power laws in its momentum distribution. The study may be extended to the case of a quantum gas initially prepared in fast rotation and relaxing towards equilibrium.

Contexte de travail

Superfluidity of quantum gases was observed soon after their first experimental realization. When set into rotation at moderate frequency, quantum vortices develop in the cloud. In the fast rotation regime, the vortices organize into a triangular vortex lattice. Recently, our group obtained a series of interesting results with a quasi two-dimensional quantum gas confined in an anharmonic trap and set into fast rotation: the observation of a highly supersonic flow and of the thermal melting of the vortex lattice. The group also developed a protocol to compensate for gravity and control the expansion of the gas on a curved surface, opening the way to the evidence of curvature effects in a two-dimensional superfluid.
The thesis project will take place within the Laboratoire de physique des lasers, a joint unit of Université Sorbonne Paris Nord and CNRS. The Bose-Einstein Condensate group (BEC group, see https://bec.lpl.univ-paris13.fr ) developed two experimental setups for the study of the dynamics of quantum gases. One of them produces routinely a rubidium quantum gas confined in a bubble-shaped trap, obtained with a combination of magnetic and radiofrequency fields. This very smooth and controlled resulting potential is ideal for the study of collectif modes and controlled rotation of the gas.
The thesis will be supervised by Hélène Perrin (DR CNRS) and co-supervised by Laurent Longchambon, associate professor of Université Sorbonne Paris Nord. A CNRS research engineer, a post-doctoral fellow and two PhD students will also be involved in the project, which is funded by agence nationale de la recherche, project PRCI RELAQS (Non-thermal fixed points during RELAxation of far-from-equilibrium Quantum gaseS), in collaboration with Vanderlei Bagnato (University of São Paulo, Brazil). The BEC group also features a CNRS researcher, an assistant professor, another postdoctoral fellow and another PhD student, mainly involved on the other experimental setup. More generally, the group belongs to the Quantum Gases research axis of LPL, with approximately 20 researchers. Beyond the already mentioned collaboration, the BEC group has regular collaboration with several experimental and theory groups, including the ones of Anna Minguzzi (LPMMC, Grenoble), Patrizia Vignolo and Sergey Nazarenko (Institut de physique de Nice), Maxim Olshanii (University of Massachusetts, Boston), Thorsten Schumm (TUW, Vienna).

Contraintes et risques

Class IV lasers: use of protection goggles in mandatory. Electric risk: high voltage.