Elliptic flow and nearly perfect fluidity in dilute Fermi gases

TL;DR

This paper reviews recent advances in understanding the shear viscosity of strongly correlated dilute Fermi gases, highlighting experimental and theoretical insights into their nearly perfect fluid behavior across different temperature regimes.

Contribution

It provides a comprehensive comparison of kinetic theory predictions with experimental data on elliptic flow and collective mode damping in dilute Fermi gases.

Findings

Agreement between theory and experiment at high temperatures

Experimental constraints on shear viscosity near quantum degeneracy

Evidence of nearly perfect fluidity with low shear viscosity to entropy ratio

Abstract

In this contribution we summarize recent progress in understanding the shear viscosity of strongly correlated dilute Fermi gases. We discuss predictions from kinetic theory, and show how these predictions can be tested using recent experimental data on elliptic flow. We find agreement between theory and experiments in the high temperature regime $T\gg T_F$, where $T_F$ is the the temperature where quantum degeneracy effects become important. In the low temperature regime, $T\sim T_F$, the strongest constraints on the shear viscosity come from experimental studies of the damping of collective modes. These experiments indicate that $\eta/s\lsim 0.5\hbar/k_B$, where $\eta$ is the shear viscosity and $s$ is the entropy density.