Quantum critical transport in the unitary Fermi gas

TL;DR

This paper investigates the transport properties of the unitary Fermi gas near a quantum critical point, calculating the shear viscosity to entropy ratio and comparing theoretical predictions with experimental data.

Contribution

It provides the first controlled calculation of ta/s in the quantum critical regime of the unitary Fermi gas using a large-N expansion.

Findings

ta/s approaches the conjectured perfect fluid limit ar/(4k_B)

The equation of state and Tan contact density C agree with recent experiments and advanced theoretical methods

The results suggest the unitary Fermi gas exhibits nearly perfect fluidity at high temperatures.

Abstract

The thermodynamic and transport properties of the unitary Fermi gas at finite temperature T are governed by a quantum critical point at T=0 and zero density. We compute the universal shear viscosity to entropy ratio \eta/s in the high-temperature quantum critical regime T>>|\mu| and find that this strongly coupled quantum fluid comes close to perfect fluidity \eta/s=\hbar/(4\pi k_B). Using a controlled large-N expansion we show that already at the first non-trivial order the equation of state and the Tan contact density C agree well with the most recent experimental measurements and theoretical Luttinger-Ward and Bold Diagrammatic Monte Carlo calculations.