Thesis defense of Antoine Ténart

Thesis defense of Antoine Ténart, PhD student in the Quantum gases group, on 09 December 2021 at 11 am in the auditorium of the Institut d'Optique in Palaiseau, on the topic: " Momentum-space correlations in the depletion of weakly interacting lattice Bose gases ".

Abstract: " In this defense, I will my present my thesis work focused on the study of the emblematic example of an interacting quantum system, the weakly-interacting Bose gas. At zero temperature, a fraction of the atoms is removed from the Bose-Einstein condensate through the interplay between the inter-particle interactions and the quantum fluctuations. This fraction is called the quantum depletion. It consists in a coherent superposition of pairs of atoms with opposite momenta, or put in other words momentum correlated atom pairs. The presence of these pairs is explained by the microscopic process of interaction between two particles. While this prediction is more than 60 years old, we report the first observation of these opposite momentum correlations in the depletion of a weakly-interacting Bose gas. To do so, we produce metastable Helium-4 condensates loaded in optical lattices. Using metastable Helium makes possible the detection of individual atoms in three dimensions after a long time-of-flight, an essential aspect to measure correlations between individual particles in momentum space. After presenting the correlation signals, we will study their main characteristics (amplitude, width, evolution with temperature) to illustrate the quantum nature of the pairing mechanism. More than confirming a theoretical prediction, these results constitute a first step in the study of many-body quantum systems at equilibrium and open the way to the study of more strongly correlated systems. "