Bogoliubov speed of sound for a dilute Bose-Einstein condensate in a 3d optical lattice

TL;DR

This paper demonstrates that the speed of sound in a 3D optical lattice Bose-Einstein condensate can reach a maximum exceeding that in a homogeneous condensate, revealing a superfluid regime accessible in experiments.

Contribution

It identifies a maximum in the sound velocity in a lattice BEC and quantifies its enhancement over homogeneous condensates, providing insights into superfluid properties in optical lattices.

Findings

Maximum sound velocity exceeds homogeneous case by 30%

Maximum occurs within the superfluid regime

Predicted effects are observable with current technology

Abstract

We point out that the velocity of propagation of sound wavepackets in a Bose-Einstein condensate filling a three-dimensional cubic optical lattice undergoes a maximum with increasing lattice depth. For a realistic choice of parameters, the maximum sound velocity in a lattice condensate can exceed the sound velocity in a homogeneous condensate with the same average density by 30%. The maximum falls into the superfluid regime, and should be observable under currently achievable laboratory conditions.