Optomechanical response of a strongly interacting Fermi gas

Helson, V.*; Zwettler, T.*; Roux, K.*; Konishi, Hideki*; Uchino, Shun; Brantut, J.-P.*

Physical Review Research (Internet), 4(3), p.033199_1 - 033199_10, 2022/09

https://doi.org/10.1103/PhysRevResearch.4.033199

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. Measuring the non-linearity as a function of interaction strength, we extract the zero-frequency density response function of the Fermi gas, and find an increase 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.