Superfluid critical velocity of a Bose-Einstein condensate in a flat potential

Specifically tailored potentials can potentially be helpful tools when investigating properties of ultra-cold gases. In this paper we study the superfluid critical velocity of Bose-Einstein condensates. Previous experimental investigations have gathered evidence for the existence of a critical velocity by moving tightly focussed optical dipole potentials [1,2] or impurities [3] through harmonically trapped Bose-Einstein condensates. However, their interpretation in terms of a critical velocity is somewhat problematic as either the potential was accelerating [1], or the speed of sound varied as a function of position due to the inhomogeneity of the condensate density [2,3]. In this paper we implement a flat-bottomed potential in order to study the superfluid critical velocity of a Bose-Einstein condensate without these limitations.