Shear Viscosity of a Unitary Fermi Gas

TL;DR

This paper provides the first ab initio quantum Monte Carlo calculations of the shear viscosity of a Unitary Fermi Gas, revealing a minimum near the superfluid transition that approaches the conjectured universal lower bound.

Contribution

It introduces a novel ab initio computational approach to determine shear viscosity in a Unitary Fermi Gas using quantum Monte Carlo and linear-response theory.

Findings

Minimum eta/s ratio is around 0.2 hbar/kB

Minimum occurs above the superfluid transition temperature

eta/s nearly saturates the Kovtun-Son-Starinets bound

Abstract

We present the first ab initio determination of the shear viscosity eta of the Unitary Fermi Gas, based on finite temperature quantum Monte Carlo calculations and the Kubo linear-response formalism. We determine the temperature dependence of the shear viscosity to entropy density ratio eta/s. The minimum of eta/s appears to be located above the critical temperature for the superfluid-to-normal phase transition with the most probable value being eta/s approx 0.2 hbar/kB, which almost saturates the Kovtun-Son-Starinets universal value hbar/(4 pi kB).