Soutenance de thèse de Roy EID

Soutenance de thèse de Roy EID, doctorant dans le groupe Gaz quantiques du Laboratoire Charles Fabry, le mardi 14 octobre 2025 à 13h30 dans l'Auditorium de l'Institut d'Optique Graduate School à Palaiseau, sur le thème : "Tunable Mean-Field and Beyond Mean-Field Interaction in a Coherently Coupled Bose-Einstein Condensate".

Résumé : "This thesis explores mean-field and beyond mean-field interactions in a coherently coupled two-component Bose-Einstein condensate (BEC) of $^{39}$K atoms. We first establish the theoretical framework describing the atomic structure of potassium-39, interatomic interactions, and Feshbach resonances. We then introduce the mean-field and beyond mean-field theories relevant to ultracold Bose gases. In addition, we describe the physics of coherently coupled two-level systems, including radio-frequency coupling, adiabatic sweeps, and scattering lengths in the dressed-state basis. A major part of the experimental work focuses on developing a high-precision magnetic field stabilization system, essential for accurate and reliable measurements in spinor BECs. We investigate the mean-field interaction energy of a coherently coupled two-component BEC in the lower dressed-state basis, both theoretically and experimentally. The results reveal nonlinearities and saturation effects as functions of density. We then explore the regime of quantum droplets, aiming at observing self-bound states stabilized by quantum fluctuations beyond the mean-field approximation. Finally, we present an experiment on BEC tunneling through optical barriers created using a Digital Micromirror Device and a blue-detuned laser, demonstrating the transition from classical to quantum tunneling and revealing Fabry–Pérot-like interference in matter waves."