Project level: Honours

Since the first experimental realization of a Bose-Einstein condensate (BEC), many of its properties have been thoroughly investigated. Superfluidity is one of the properties of a BEC which is yet not fully understood. Previous experimental investigations have gathered evidence for the existence of a critical velocity by moving tightly focussed optical dipole potentials or impurities through harmonically trapped Bose-Einstein condensates. However, their interpretation in terms of a critical velocity is somewhat problematic as either the potential was accelerating, or the speed of sound varied as a function of position due to the inhomogeneity of the condensate density. Specifically tailored potentials are helpful tools when investigating properties of ultra-cold gases. We will use our versatile, time-averaged trapping scheme to create a ring-shaped potential for a BEC in order to quantitatively determine the critical velocity of such a system. Here, a flat-bottomed trap is generated by rapidly scanning the focussed laser in a circle, and the barrier is formed by reducing the laser power at a dynamically controllable position. By varying the speed of the barrier and observing the behavior of the BEC, we will quantitatively determine the critical velocity of this system.

Project members

Dr Mark Baker

Research Fellow