Excitations of a Bose-Einstein Condensate at Non-Zero Temperature: A Study of Zeroth, First and Second Sound

摘要

Collective excitations of a dilute Bose gas were probed above and below theBose-Einstein condensation temperature. The temperature dependencies of thefrequency and damping rates of condensate oscillations indicate significantinteractions between the condensate and the thermal cloud. Hydrodynamicoscillations of the thermal cloud were observed, constituting first sound. Anantisymmetric dipolar oscillation of the thermal cloud and the condensate wasstudied, representing the bulk flow of a superfluid through the normal fluid.The excitations were observed in situ using non-destructive imaging techniques.