A Spectroscopic Method to Measure the Superfluid Fraction of an Ultracold Atomic Gas

TL;DR

This paper analyzes a spectroscopic method to measure the superfluid fraction in ultracold atomic gases, accounting for temperature and interactions, demonstrating its effectiveness in different regimes.

Contribution

It extends previous theoretical work by including temperature and interaction effects, assessing the method's accuracy for various Bose gases.

Findings

Method yields detectable signals under suitable conditions.

Superfluid fraction closely follows condensate fraction below critical temperature.

Differentiates superfluid and condensate densities in strongly interacting gases.

Abstract

We perform detailed analytical and numerical studies of a recently proposed method for a spectroscopic measurement of the superfluid fraction of an ultracold atomic gas [N. R. Cooper and Z. Hadzibabic, Phys. Rev. Lett. 104, 030401 (2010)]. Previous theoretical work is extended by explicitly including the effects of non-zero temperature and interactions, and assessing the quantitative accuracy of the proposed measurement for a one-component Bose gas. We show that for suitably chosen experimental parameters the method yields an experimentally detectable signal and a sufficiently accurate measurement. This is illustrated by explicitly considering two key examples: First, for a weakly interacting three-dimensional Bose gas it reproduces the expected result that below the critical temperature the superfluid fraction closely follows the condensate fraction. Second, it allows a clear quantitative differentiation of the superfluid and the condensate density in a strongly interacting Bose gas.