Breakdown of superfluidity of an atom laser past an obstacle

TL;DR

This paper investigates the conditions under which a 1D Bose-Einstein condensate atom laser flow remains superfluid or becomes dissipative when encountering obstacles, highlighting the effects of obstacle type and flow velocity.

Contribution

It provides a detailed analysis of superfluidity breakdown in atom lasers, including the critical velocity and the impact of obstacle potential type, extending Landau's theory to this context.

Findings

Critical velocity can reach Landau's prediction for attractive obstacles.

Superfluidity is recovered at high velocities for penetrable obstacles.

Significant drag differences occur between repulsive and attractive potentials.

Abstract

The 1D flow of a continuous beam of Bose-Einstein condensed atoms in the presence of an obstacle is studied as a function of the beam velocity and of the type of perturbing potential (representing the interaction of the obstacle with the atoms of the beam). We identify the relevant regimes: stationary/time-dependent and superfluid/dissipative; the absence of drag is used as a criterion for superfluidity. There exists a critical velocity below which the flow is superfluid. For attractive obstacles, we show that this critical velocity can reach the value predicted by Landau's approach. For penetrable obstacles, it is shown that superfluidity is recovered at large beam velocity. Finally, enormous differences in drag occur when switching from repulsive to attractive potential.