Une nouvelle expérience d'atomes ultrafroids pour étudier la dynamique de relaxation dans les gaz quantiques en interaction

par Clémence Briosne Frejaville

Projet de thèse en Physique quantique

Sous la direction de Christoph Westbrook et de Marc Cheneau.

Thèses en préparation à Paris Saclay , dans le cadre de Ondes et Matière , en partenariat avec Laboratoire Charles Fabry (laboratoire) , Optique atomique (equipe de recherche) et de Institut d'optique théorique et appliquée (Orsay, Essonne) (établissement de préparation de la thèse) depuis le 01-10-2017 .

  • Résumé

    Statistical mechanics is one of the most powerful constructions of physics. It predicts that the equilibrium properties of any system composed of a large number of particles depend only on a handful of macroscopic parameters, no matter how the particles exactly interact with each other. But the question of how many-body systems relax towards such equilibrium states remains largely unsolved. This problem is especially acute for quantum systems, which evolve in a much larger mathematical space than the classical space-time and obey non- local equations of motion. Despite the formidable complexity of quantum dynamics, recent theoretical advances have put forward a very simple picture: the dynamics of quantum many-body systems would be essentially local, meaning that it would take a finite time for correlations between two distant regions of space to reach their equilibrium value. This locality would be an emergent collective property, similar to spontaneous symmetry breaking, and have its origin in the propagation of quasiparticle excitations. The fact is, however, that only few observations directly confirm this scenario. In particular, the role played by the dimensionality and the range of the interaction potential between the particles is largely unknown. The concept of our research is to take advantage of the great versatility offered by ultracold atom systems to investigate experimentally the relaxation dynamics in regimes well beyond the boundaries of our current knowledge. We are planning the construction of a new-generation quantum gas microscope experiment for strontium gases. Among the innovative experimental techniques that we will implement is the electronic state hybridization with Rydberg states, called Rydberg dressing.

  • Titre traduit

    A new ultracold atom apparatus for investigating the relaxation dynamics of quantum many-body systems

  • Résumé

    The PhD student will first have in charge the construction of this new experimental apparatus, starting with setting up the laser system for cooling the strontium gas, designing and assembling the vacuum chamber in which the experiments will later be performed, and achieving the Bose–Einstein condensation of the sample in a dipolar trap. The next stage will be to obtain fluorescence images of the atoms in an optical lattice with single- atom sensitivity and single-site resolution. Such images have already been obtained in a handful of groups worldwide but using different atomic species. Imaging strontium with such accuracy will be a premiere. Once the experimental apparatus will be operational, the PhD student will have the opportunity to perform several experiments to characterize the relaxation dynamics of the gas. These experiments will always follow the same logic: first, the sample will be prepared in some state chosen as initial state for the dynamics. Then, the system will be left to evolve coherently under the sole effect of the interactions between the atoms. Finally, the state of the system will be recorded via a fluorescence image of the atom spatial distribution and characterized by the evaluation of two-point correlation functions. Varying the initial state, the geometry of the system and the nature of the interactions will allow the student to find out which properties of the relaxation dynamics are generic and what is their microscopic origin.