Hydrodynamic expansion of a strongly interacting Fermi-Fermi mixture

Abstract

We report on the expansion of an ultracold Fermi-Fermi mixture of Li6 and K40 under conditions of strong interactions controlled via an interspecies Feshbach resonance. We study the expansion of the mixture after release from the trap and, in a narrow magnetic-field range, we observe two phenomena related to hydrodynamic behavior. The common inversion of the aspect ratio is found to be accompanied by a collective effect where both species stick together and expand jointly despite of their widely different masses. Our work constitutes a major experimental step for a controlled investigation of the many-body physics of this novel strongly interacting quantum system. © 2011 American Physical Society.