Influence of quantum fluctuations on the superfluid critical velocity of a one-dimensional Bose gas

TL;DR

This paper investigates how quantum fluctuations affect the critical velocity for superfluid flow in a one-dimensional Bose gas, revealing probabilistic soliton formation and momentum transfer mechanisms beyond mean-field theory.

Contribution

It introduces a beyond-mean-field analysis using the truncated Wigner approximation to study quantum fluctuation effects on superfluid critical velocity in a 1D Bose gas.

Findings

Quantum fluctuations induce probabilistic grey soliton formation.

Soliton cascades lead to rapid fluid acceleration.

Momentum transfer relates to macroscopic tunnelling between flow states.

Abstract

The mean-field Gross-Pitaevskii equation with repulsive interactions exhibits frictionless flow when stirred by an obstacle below a critical velocity. Here we go beyond the mean-field approximation to examine the influence of quantum fluctuations on this threshold behaviour in a one-dimensional Bose gas in a ring. Using the truncated Wigner approximation, we perform simulations of ensembles of trajectories where the Bose gas is stirred with a repulsive obstacle below the mean-field critical velocity. We observe the probabilistic formation of grey solitons which subsequently decay, leading to an increase in the momentum of the fluid. The formation of the first soliton leads to a soliton cascade, such that the fluid rapidly accelerates to minimise the speed difference with the obstacle. We measure the initial rate of momentum transfer, and relate it to macroscopic tunnelling between quantised flow states in the ring.