Beyond-mean-field effects in ultracold gases
Ultracold gases are well controllable quantum systems that are described by a set of few parameters. The idea to look at systems with partially attractive and repulsive forces, fine-tuned to an approximate overall cancellation of the mean-field term, provide an interesting platform for studying various beyond-mean-field phenomena, remarkable recent examples being quantum droplets and dipolar supersolids. In this thesis, we take a step towards understanding the phase diagram of the 1D Bose-Bose mixture with attractive interspecies and repulsive intraspecies contact interactions. We address the one-dimensional three-body problem with two- and three-body interactions that we solve analytically. Then, we develop the perturbation theory for systems with a weak two-body potential interaction, where the attractive and repulsive parts compensate each other. We calculate in every dimension the leading nonpairwise contribution, which represents an effective three-body interaction. We apply this result particularly to tilted dipoles in quasi-low-dimensional geometries. Interestingly, we show the consistency of this few-body perturbative approach with the Bogoliubov one.
Frédéric Chevy, LKB ENS, Paris, examinateur
Mario Gattobigio, INPHYNI, Nice, rapporteur
Denis Lacroix, IJCLab, Orsay, examinateur
Dmitry Petrov, LPTMS, Orsay, directeur de thèse
Luis Santos, Leibniz Universität Hannover, rapporteur
Leticia Tarruel, ICFO, Barcelona, examinatrice