Normal state of a polarized Fermi gas at unitarity

TL;DR

This paper investigates the properties of a polarized Fermi gas at unitarity at zero temperature, using quantum Monte Carlo methods to determine its equation of state, effective mass, and phase transition characteristics.

Contribution

It provides the first detailed quantum Monte Carlo calculations of the normal phase of a polarized Fermi gas at unitarity, including the equation of state and phase transition predictions.

Findings

First order phase transition at x_c=0.44

Critical polarization P_c=77% in harmonic traps

Interaction increases spin dipole mode frequency by 23%

Abstract

We study the Fermi gas at unitarity and at T=0 by assuming that, at high polarizations, it is a normal Fermi liquid composed of weakly interacting quasiparticles associated with the minority spin atoms. With a quantum Monte Carlo approach we calculate their effective mass and binding energy, as well as the full equation of state of the normal phase as a function of the concentration x=n_\down/n_\up of minority atoms. We predict a first order phase transition from normal to superfluid at x_c=0.44 corresponding, in the presence of harmonic trapping, to a critical polarization P_c=(N_\up-N_\down)/ (N_\up+N_\down)=77%. We calculate the radii and the density profiles in the trap and predict that the frequency of the spin dipole mode will be increased by a factor of 1.23 due to interactions.