Critical Velocity in a Bose Gas in a Moving Optical Lattice at Finite Temperatures

TL;DR

This paper investigates how the critical velocity of a Bose-condensed gas in a moving optical lattice decreases with increasing temperature and lattice depth, using theoretical calculations that align with experimental results.

Contribution

It provides a detailed theoretical analysis of the critical velocity at finite temperatures, incorporating thermal excitations and radial effects, which were previously neglected.

Findings

Critical velocity decreases rapidly with increasing temperature.

Critical velocity drops significantly with increasing lattice depth.

Thermal excitations in the radial direction strongly influence the critical velocity.

Abstract

We study the critical velocity of a Bose-condensed gas in a moving one-dimensional (1D) optical lattice potential at finite temperatures. Solving the Gross-Pitaeavskii equation and the Bogoliubov equations, within the Popov approximation, we calculate the Bogoliubov excitations with varying lattice velocity. From the condition of the negative excitation energy, we determine the critical velocity as a function of the lattice depth and the temperature. We find that the critical velocity decreases rapidly with increasing the temperature; this result is consistent with the experimental observations. Moreover, the critical velocity shows a rapid decrease with increasing lattice depth. This tendency is much more significant than in the previous works ignoring the effect of thermal excitations in the radial direction.