Pseudogap effects in the unitary Fermi gas and in strongly interacting 2D Fermi gases*

Understanding of the unitary Fermi gas of infinite scattering length presents a major challenge owing to the presence of strong correlations. In particular, the existence and extent of a pseudogap regime, in which pairing correlations persist above the superfluid critical temperature, has been extensively debated in the literature. We address the pseudogap question using auxiliary-field quantum Monte Carlo methods on the lattice, optimized to enable large lattice calculations of thermodynamic observables. In particular, we calculate a model-independent energy-staggering pairing gap, which avoids an ill-posed numerical analytic continuation. We extrapolate to the continuum limit, thereby removing finite effective range effects. We use similar methods to study pseudogap effects in interacting 2D Fermi gases along the Bardeen-Cooper-Schrieffer (BCS) to Bose-Einstein condensation (BEC) crossover. Our results provide a benchmark for experiments and other strong coupling methods.