# Effective-range dependence of resonant Fermi gases

## TL;DR

This study investigates how the effective range of interactions influences the properties of a resonant Fermi gas, providing new computational methods and identifying stability limits.

## Contribution

We developed a pseudopotential formalism for smooth potentials with variable effective range and applied Monte Carlo methods to analyze the ground state of a unitary Fermi gas.

## Key findings

- Universal constants: ξ = 0.388(1), ζ = 0.087(1)
- Computed condensate fraction, momentum distribution, and pair correlations
- Identified thermodynamic instability for k_F R_eff ≥ 1.9

## Abstract

A Fermi gas of cold atoms allows precise control over the dimensionless effective range, $k_\mathrm{F} R_\mathrm{eff}$, of the Feshbach resonance. Our pseudopotential formalism allows us to create smooth potentials with effective range, $-2 \leq k_\mathrm{F} R_\mathrm{eff} \leq 2$, 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 $\xi = 0.388(1)$ and $\zeta = 0.087(1)$, and compute the condensate fraction, momentum distribution, and pair correlations functions. Finally, we show that a gas with $k_\mathrm{F} R_\mathrm{eff} \gtrsim 1.9$ is thermodynamically unstable.