Description du sujet de thèse

The aim of the PhD project is to demonstrate the presence of solitons in one-dimensional (1D) weakly interacting Bose gases at finite temperature or following dynamic excitation. The gas can be described by a wave function, or equivalently by a density and a phase. A soliton corresponds to a local density depletion that propagates within the gas without dispersion. It is associated with a phase shift distributed along its extension, the latter being fixed by the system's healing length. The presence of solitons in the system can be revealed by direct imaging or by the shape of the gas velocity distribution. The objective of this thesis project is to study the out-of-equilibrium dynamics of a weakly interacting Bose gas confined in a box trap under strong excitation, and to evidence the presence of solitons in the gas. While the project is mainly experimental, it may also include numerical simulations of these phenomena.

Contexte de travail

The activity will take place at Laboratoire de Physique des Lasers, a joint research unit of Université Sorbonne Paris Nord and CNRS. The Bose-Einstein Condensate group (BEC group, see https://bec.lpl.univ-paris13.fr/ ) has developed two experiments on the dynamics of quantum gases. The experiment on which the project will be based routinely produces a sodium quantum gas confined in a highly anisotropic harmonic potential. At low temperatures and for gases of a few thousand atoms, the system enters the one-dimensional regime, the energy scale of transverse excitations being higher than the characteristic energies of the gas.

The thesis will be directed by Hélène Perrin (DR CNRS) and co-supervised by Aurélien Perrin (CR CNRS). A lecturer, a post-doc and a PhD student will also be involved in the project, which is funded by the France 2030 program, PEPR project Dyn1D (Dynamics out of ́equilibrium of one-dimensional quantum gases), in collaboration with 10 other research groups mixing theoreticians and experimentalists. In addition, the BEC group includes another lecturer, a research engineer, two PhD students and a post-doc, mainly involved on the other experimental set-up. The group is part of the laboratory's Quantum Gases axis, which brings together some twenty researchers. In addition to those already mentioned in the context of this project, the BEC team has forged collaborations with several experimental and theoretical groups, including Anna Minguzzi at the LPMMC in Grenoble, Patrizia Vignolo and Sergey Nazarenko at the Institut de Physique in Nice, Maxim Olshanii at the University of Massachusetts in Boston, and Thorsten Schumm at the TUW University in Vienna.

Le poste se situe dans un secteur relevant de la protection du potentiel scientifique et technique (PPST), et nécessite donc, conformément à la réglementation, que votre arrivée soit autorisée par l'autorité compétente du MESR.

Contraintes et risques

Class IV laser: safety goggles must be worn. Electrical hazards: use of high voltage.