Daniel Pérez Cruz
 “Superfluid fraction in disordered quantum fluids”

Abstract

An ultracold dilute gas of bosons can have a fraction of its components in the so-called superfluid state. A superfluid exhibits a series of counter-intuitive properties that are closely related to those of superconductors. As examples we can mention the non-classical rotational moment of inertia, the quantization of vorticity, and the capacity to flow without losses. Determining the superfluid fraction in an actual experiment with ultracold atoms is a non-trivial task. In a series of papers, A. Leggett derived strict upper and lower bounds for this quantity in terms of the local density of particles. Here we study numerically the superfluid fraction of a gas in both optical lattices and disordered (speckle) potentials in one and two spatial dimensions, directly comparing our numerical results to the aforementioned bounds.