Sound propagation in a Bose-Einstein condensate at finite temperatures

TL;DR

This paper investigates how sound waves travel in a Bose-Einstein condensate at finite temperatures, using imaging techniques to measure the speed of sound and comparing it with theoretical models.

Contribution

It provides experimental validation of the Landau two-fluid model for sound propagation in Bose-Einstein condensates at finite temperatures.

Findings

Speed of sound matches Landau two-fluid model predictions

Density waves can be observed with phase-contrast imaging

Temperature dependence of sound speed characterized

Abstract

We study the propagation of a density wave in a magnetically trapped Bose-Einstein condensate at finite temperatures. The thermal cloud is in the hydrodynamic regime and the system is therefore described by the two-fluid model. A phase-contrast imaging technique is used to image the cloud of atoms and allows us to observe small density excitations. The propagation of the density wave in the condensate is used to determine the speed of sound as a function of the temperature. We find the speed of sound to be in good agreement with calculations based on the Landau two-fluid model.