Tunable viscosity across the BCS-BEC crossover

TL;DR

This paper proposes a method to enhance Reynolds numbers in ultracold Fermi gases by tuning shear viscosity near Feshbach resonances, enabling tabletop turbulence studies.

Contribution

It theoretically demonstrates that shear viscosity can vary significantly near the BCS-BEC crossover, providing a way to control turbulence conditions in ultracold gases.

Findings

Shear viscosity varies by orders of magnitude near the BCS-BEC crossover.

Higher-order vertex corrections suppress singular behavior near resonance.

Tunable Reynolds numbers can be achieved for turbulence simulation.

Abstract

Tunable interactions make ultracold quantum gases a unique platform for exploring hydrodynamic properties in the strongly correlated regime. Of particular interest are turbulent flows possible in the regime of high Reynolds numbers. Since the system size and flow velocity are limited in experimentally realistic systems, we propose an alternative approach to enhance the Reynolds numbers in an ultracold Fermi gas by minimizing the shear viscosity in the vicinity of the Feshbach resonance. By employing the Keldysh formulation of the linear response theory, we theoretically demonstrate that the shear viscosity can vary by several orders of magnitude in the vicinity of the BCS-BEC crossover. It is also shown that while Drude-like contributions generally dominate at large Feshbach detunings, higher-order vertex corrections, including the Maki-Thompson contribution, become significant and suppress singular behavior in the near-resonant regime. Our results provide a roadmap for achieving tunable Reynolds numbers in ultracold quantum fluids, which can serve as table-top turbulence simulators.