Effective-range dependence of resonant Fermi gases

Abstract

A Fermi gas of cold atoms allows precise control over the dimensionless effective range, $\textbf{kFReff}$, of the Feshbach resonance. Our pseudopotential formalism allows us to create smooth potentials with effective range, $\textbf{-2≤kFReff≤2}$, which we use for a variational and diffusion Monte Carlo study of the ground state of a unitary Fermi gas. We report values for the universal constants of $\textbf{ξ=0.388(1)}$ and $\textbf{ζ=0.087(1)}$, and compute the condensate fraction, momentum distribution, and pair correlations functions. Finally, we show that a gas with $\textbf{kFReff1.9}$ is thermodynamically unstable.