Cooper pair turbulence in atomic Fermi gases

TL;DR

This paper studies the stability of uniform fermionic superfluids, revealing that large systems develop spatial instabilities leading to a turbulent state with random superpositions of pairing modes, which can be experimentally probed.

Contribution

It demonstrates the instability of uniform solutions in large fermionic superfluids and characterizes the resulting turbulent state caused by parametric excitations.

Findings

Spatial fluctuations destabilize uniform superfluid solutions in large systems.

Nonlinear effects suppress growth of modulations, leading to turbulence.

Proposes spectroscopic noise as a probe for the turbulent state.

Abstract

We investigate the stability of spatially uniform solutions for the collisionless dynamics of a fermionic superfluid. We demonstrate that, if the system size is larger than the superfluid coherence length, the solution characterized by a periodic in time order parameter is unstable with respect to spatial fluctuations. The instability is due to the parametric excitations of pairing modes with opposite momenta. The growth of spatial modulations is suppressed by nonlinear effects resulting in a state characterized by a random superposition of wave packets of the superfluid order parameter. We suggest that this state can be probed by spectroscopic noise measurements.