Viscosity of Strongly Interacting Fermi Gases

Transport in strongly interacting systems, which may not support well-defined quasiparticle excitations, is a subject of great interest in diverse fields ranging from condensed matter, atomic-molecular and nuclear physics to string theory. I will begin with a brief review of the unitary Fermi gas which lies at the center of the BCS-to-BEC crossover. The measured shear viscosity to entropy density ratio in the unitary
Fermi gas comes close to saturating a conjectured lower bound.

I will then describe recent work [1] on the bulk and shear viscosity of non-relativistic quantum fluids, with a particular focus on strongly interacting ultracold Fermi gases. I will discuss exact non-perturbative results based on spectral functions and sum rules, and conclude with a proposal for a spectroscopic measurement of the shear viscosity spectral function in the unitary Fermi gas.

[1] E. Taylor and M. Randeria, arXiv:1002:0869.