Equation of State of a Fermi Gas in the BEC-BCS Crossover: A Quantum Monte Carlo Study

We calculate the equation of state of a two-component Fermi gas with attractive short-range interspecies interactions using the fixed-node diffusion Monte Carlo method. The interaction strength is varied over a wide range by tuning the value $a$ of the $s$-wave scattering length of the two-body potential. For $a>0$ and $a$ smaller than the inverse Fermi wave vector our results show a molecular regime with repulsive interactions well described by the dimer-dimer scattering length $a_m=0.6a$. The pair correlation functions of parallel and opposite spins are also discussed as a function of the interaction strength.