Université Sorbonne, France
Quantum gases provide us with a very convenient and widely tunable system for the study of superfluidity. In particular, they can be confined in a large variety of geometries (harmonic traps, optical lattices, box traps, lower dimensional traps…), enabling the study of superfluid dynamics with specific constrains. In this talk I will present the behaviour of a superfluid quantum gas confined at the surface of an ellipsoid: the atoms can move freely in directions parallel to the surface and are strongly confined in the transverse direction. In a first series of experiments, the atoms initially at rest at the bottom of the shell -because of gravity- are set into rotation: a vortex lattice develops at moderate rotation, and melts for large rotation speeds or low atom numbers. We explore the transition from a vortex crystal to a disordered vortex and eventually random phase fluctuations. In a second series of experiment, we implement a way to compensate gravity on the shell. We evidence new effects that prevent the atoms to fill the entire shell, leading to an annular density distribution at equilibrium. These effects are of high relevance to microgravity shell experiments, as performed in particular in the ISS.