Critical superfluid velocity in a trapped dipolar gas

TL;DR

This paper studies the superfluid critical velocity in a trapped dipolar Bose-Einstein condensate, linking the roton spectrum to superfluidity limits and proposing an experiment to observe these effects.

Contribution

It calculates the superfluid critical velocity using the Landau criterion for a 3D dipolar BEC and proposes an experiment to measure it and detect the roton spectrum.

Findings

Roton spectrum lowers the critical velocity beyond a critical particle number.

The shape of the dispersion and roton minimum are tunable via particle number.

Proposes an experiment to measure the Landau critical velocity and observe the roton.

Abstract

We investigate the superfluid properties of a dipolar Bose-Einstein condensate (BEC) in a fully three-dimensional trap. Specifically, we calculate 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.