Quantum Monte Carlo Studies of Superfluid Fermi Gases

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We report results of quantum Monte Carlo calculations of the ground state of dilute Fermi gases with attractive short range two-body interactions. The strength of the interaction is varied to study different pairing regimes which are characterized by the product of the s-wave scattering length and the Fermi wave vector, akF. We report results for the ground state energy, the pairing gap Δ and the quasiparticle spectrum. In the weak coupling regime, 1/akF < -1, we obtain BCS superfluid and the energy gap Δ is much smaller than the Fermi gas energy EFG. When a > 0, the interaction is strong enough to form bound molecules with energy Emol. For 1/akF 0.5 we find that weakly interacting composite bosons are formed in the superfluid gas with Δ and gas energy per particle approaching |Emol|/2. In this region we seem to have Bose-Einstein condensation (BEC) of molecules. The behavior of the energy and the gap in the BCS to BEC transition region, -0.5 < 1/akF < 0.5 is discussed.