Superfluidity in Gases and Liquids

The first lecture deals with Bose-Einstein Condensation (BEC) and Superfluidity in gases and liquids. It starts with the direct observation of long-range phase coherence in a trapped gas and discusses why the ground state of any fluid phase of Bosons always exhibits BEC. Gaseous and liquid states turn out to be separated by a quantum tricritical point which appears at vanishing scattering length. In its vicinity, self-bound liquid droplets of Bosons are stabilized by three-body repulsion. The associated unbinding of N-body bound states at a geometric sequence of scattering lengths extends the Efimov effect at N=3 to arbitrary N.