title: Critical superfluid velocity in a trapped dipolar gas.
abstract: We investigate the superfluid properties of a dipolar Bose-Einstein condensate (BEC) in a fully three-dimensional trap. Specifically, we estimate a superfluid critical velocity for this system by applying the Landau criterion to its discrete quasiparticle spectrum. We test this critical velocity by direct numerical simulation of condensate depletion as a blue-detuned laser moves through the condensate. In both cases, the presence of the roton in the spectrum serves to lower the critical velocity beyond a critical particle number. Since the shape of the dispersion, and hence the roton minimum, is tunable as a function of particle number, we thereby propose an experiment that can simultaneously measure the Landau critical velocity of a dipolar BEC and demonstrate the presence of the roton in this system.
authors.affiliation: JILA and Department of Physics, University of Colorado, Boulder, Colorado 80309-0440, USA. rmw@colorado.edu
authors.forename: Ryan M
authors.initials: RM
authors.lastname: Wilson
authors.forename: Shai
authors.initials: S
authors.lastname: Ronen
authors.forename: John L
authors.initials: JL
authors.lastname: Bohn