# Viscosity of strongly interacting quantum fluids: spectral functions and sum rules - Condensed Matter > Quantum Gases

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Abstract: The viscosity of strongly interacting systems is a topic of great interest indiverse fields.We focus here on the bulk and shear viscosities of \emph{non-relativistic}quantum fluids, with particular emphasis on strongly interacting ultracoldFermi gases. We use Kubo formulas for the bulk and shear viscosity spectralfunctions, $\zeta\omega$ and $\eta\omega$ respectively, to derive exact,non-perturbative results. Our results include: a microscopic connection betweenthe shear viscosity $\eta$ and the normal fluid density $ho n$; sum rules for$\zeta\omega$ and $\eta\omega$ and their evolution through the BCS-BECcrossover; universal high-frequency tails for $\eta\omega$ and the dynamicstructure factor $S{\bf q}, \omega$. We use our sum rules to show that, atunitarity, $\zeta\omega$ is identically zero and thus relate $\eta\omega$to density-density correlations. We predict that frequency-dependent shearviscosity $\eta\omega$ of the unitary Fermi gas can be experimentallymeasured using Bragg spectroscopy.

Autor: Edward Taylor, Mohit Randeria

Fuente: https://arxiv.org/