Leticia Tarruell

Self-bound states appear in contexts as diverse as solitary waves in channels, optical solitons in non-linear media and liquid droplets. Their binding results from a balance between attractive forces, which tend to make the system collapse, and repulsive ones, which stabilize it to a finite size.In this talk, I will present experiments on dilute quantum liquid droplets: macroscopic clusters of ultra-cold atoms that are eight orders of magnitude more dilute than liquid Helium, but have similar liquid-like properties. We have observed these droplets in a mixture of Bose-Einstein condensates with effective attractive interactions, and mapped out the associated liquid-to-gas transition. In a second series of experiments, we have placed such droplets in an optical waveguide and explored their connection to more conventional bright solitons.Finally, in ongoing experiments we are studying how the properties of the system are modified in the presence of a coherent coupling between the two components. Interestingly, the existence of dilute quantum droplets is a direct result of quantum fluctuations. Thus, their properties constitute a sensitive test of quantum many-body theories.