Shock waves in strongly interacting Fermi gas from time-dependent density functional calculations

TL;DR

This paper uses density functional calculations to simulate shock waves in strongly interacting Fermi gases, showing that dispersive effects, rather than viscosity, explain experimental observations of cloud collisions.

Contribution

It introduces a superfluid hydrodynamics model with quantum gradient terms to accurately reproduce experimental collision dynamics without invoking viscosity.

Findings

Quantitative agreement with experiments using dispersive hydrodynamics

Dispersive density ripples can be observed under certain initial conditions

Viscosity is not necessary to explain shock wave phenomena in this system

Abstract

Motivated by a recent experiment [Phys. Rev. Lett. 106, 150401 (2011)] we simulate the collision between two clouds of cold Fermi gas at unitarity conditions by using an extended Thomas-Fermi density functional. At variance with the current interpretation of the experiments, where the role of viscosity is emphasized, we find that a quantitative agreement with the experimental observation of the dynamics of the cloud collisions is obtained within our superfluid effective hydrodynamics approach, where density variations during the collision are controlled by a purely dispersive quantum gradient term. We also suggest different initial conditions where dispersive density ripples can be detected with the available experimental spatial resolution.