Optomechanical Response of a Strongly Interacting Fermi Gas

TL;DR

This paper investigates the optomechanical response of a strongly interacting Fermi gas coupled to an optical cavity, revealing a tunable nonlinear Kerr effect linked to the gas's density response and interaction strength.

Contribution

It demonstrates the measurement of the density response function across interaction regimes and confirms theoretical predictions based on universal functions of interactions.

Findings

Density response doubles from BCS to BEC regime

Strong optomechanical Kerr nonlinearity observed

Results agree with operator-product expansion theory

Abstract

We study a Fermi gas with strong, tunable interactions dispersively coupled to a high-finesse cavity. Upon probing the system along the cavity axis, we observe a strong optomechanical Kerr nonlinearity originating from the density response of the gas to the intracavity field and measure it as a function of interaction strength. We find that the zero-frequency density response function of the Fermi gas increases by a factor of two from the Bardeen-Cooper-Schrieffer to the Bose-Einstein condensate regime. The results are in quantitative agreement with a theory based on operator-product expansion, expressing the density response in terms of universal functions of the interactions, the contact and the internal energy of the gas. This provides an example of a driven-dissipative, strongly correlated system with a strong nonlinear response, opening up perspectives for the sensing of weak perturbations or inducing long-range interactions in Fermi gases.