Faraday Waves in strongly interacting superfluids

TL;DR

This paper reports the experimental observation of Faraday waves in a strongly interacting Fermi superfluid, analyzing their behavior across different interaction regimes and comparing results with theoretical models.

Contribution

It provides the first detailed characterization of Faraday waves in a strongly interacting Fermi superfluid across the BEC-BCS crossover, including stability analysis and effective sound speed measurements.

Findings

Faraday wave visibility decreases approaching unitarity

Effective 1D speed of sound matches numerical simulations

Faraday waves emerge as unstable solutions in a Mathieu-like model

Abstract

We report on the observation of Faraday waves in a cigar-shaped Fermi superfluid of $^6$Li parametrically excited by modulating the radial trap frequency. We characterize the phenomenon as a function of the interaction parameter by means of a Feshbach resonance. Starting from the BEC side of the resonance we observe a drop on the visibility of the Faraday pattern as we approach to unitarity, possibly due to the increased incompressibility of the system. We probe the superfluid excitation spectrum by extracting an effective 1D speed of sound for different values of the interaction parameter, in good agreement with numerical simulations. Finally, we perform a stability analysis in the parameter space using a simplified model and we show the emergence of the Faraday waves as unstable solutions to a Mathieu-like equation.