Thesis defense of Lucas LAVOINE

Thesis defense of Lucas LAVOINE, PhD student in the Quantum Gases group at the Charles Fabry Laboratory, on 13 October 2022 at 2pm in the Auditorium of the Institut d'Optique de Palaiseau (and by videoconference), on the topic: "Spin Mixture of Bose-Einstein condensate: Quantum droplets and Coherent Coupling".

Abstract: "The high degree of control of ultracold atoms has made these systems ideal candidates to identify and measure the role of quantum fluctuations. For a Bose-Einstein condensate, quantum fluctuations cause quantum depletion and lead to the Lee-Huang-Yang (LHY) correction in the mean field equation of state. Recently, quantum droplets formation using spin mixtures has been theoretically predicted and observed experimentally. This doctoral thesis is part of these studies.  Experimentally, we use a quantum bosonic gas of potassium 39 which offers the possibility to tune interatomic interactions using Feshbach resonances. This presentation presents two experimental studies where we explored coherently coupled spin mixtures whose intra spin interactions are repulsive and inter spin attractive. The first analysis shows the possibility of engineering an attractive three-body interaction with important consequences on the system dynamics. It originates from the spinor degree of freedom that is affected by a two-body mean-field shift of the driven transition frequency. We finally study in an experimental configuration where the mean field interactions are canceled, the beyond-mean-field equation of state of a coherently coupled two-component condensates. We show that the presence of the coupling changes the density dependence of the quantum fluctuations term with respect to the LHY term in the uncoupled case."