Evidence for a Critical Velocity in a Bose-Einstein Condensed Gas (original) (raw)

We have studied dissipation in a Bose-Einstein condensed gas by moving a blue detuned laser beam through the condensate at different velocities. Strong heating was observed only above a critical velocity. PACS numbers: 03.75.Fi, 67.40.Vs, 67.57.De Macroscopic quantum coherence and collective excitations are key features in our understanding of the phenomenon of superfluidity. The superfluid velocity is proportional to the gradient of the phase of a macroscopic wave function. Collective excitations determine a critical velocity below which the flow is dissipationless. This velocity is given by Landau's criterion ,