Characterisation of Transport in Bose-Einstein Condensates Below and Above the Critical Velocity

Abstract

Five experiments are performed to characterise the time development of the chemical potential and temperature of a bimodal Bose-condensed gas. The five experiments are a stationary experiment, a slow motion experiment, a slow motion over a barrier experiment, a fast motion experiment and a fast motion over a barrier experiment. In the two slow motion experiments the atoms are moved with velocities below the critical velocity of superfluidity, while in the two fast motion experiments the atoms are moved with velocities above the critical velocity. We observed superfluidity in the slow slow motion experiments. Additional heating was observed in fast motion experiments, indicating that the system is not superfluid in this regime. Furthermore we find transition temperatures for the five experiments. Below this transition temperature, heating of the system occurs and above, cooling of the system occurs. For the stationary experiment, the transition temperature is found to be approximately 719 nK.