Equation of State of Fermi Polarons

Fermi polarons are spin impurities dressed by interactions with a fermionic bath: an extension of the classic polaron problem where an electron is coupled to a sea of phonons. Here we present thermodynamic measurements of strongly interacting Fermi gases in the polaronic regime. We trap spin-imbalanced $^6$Li gases in a hybrid potential that is harmonic in one dimension and uniform in the other two, allowing us to extract local thermodynamic quantities with high signal to noise. The density and compressibility of the majority spin component are observed to deviate from the ideal Fermi gas. In addition, we report progress towards the gradual “undressing” of the Fermi polarons as the temperature is increased.