Measuring the Superfluid Fraction of an Ultracold Atomic Gas
Central to the understanding of the physics of degenerate Bose gases are the concepts of Bose-Einstein condensation and superfluidity. Both phenomena admit clear quantitative definitions, allowing a Bose gas to be characterised by "condensate'' and "superfluid'' fractions. For ultra-cold atomic Bose gases, the condensate fraction is readily measured through the mapping of occupation numbers in momentum space to real space by expansion imaging. While characteristic signatures of superfluidity have been observed in atomic gases, there has been no quantitative measurement of the superfluid fraction. I will describe how the superfluid fraction of an atomic gas could be measured using a light-induced vector potential, as pioneered in recent work at NIST. The proposed method is closely analogous to the classic experimental method of Andronikashvili for measuring the superfluid fraction of liquid helium.