  The Quantum Monte Carlo method for spin 1/2 fermions at finite temperature is
formulated for dilute systems with an s-wave interaction. The motivation and
the formalism are discussed along with descriptions of the algorithm and
various numerical issues. We report on results for the energy, entropy and
chemical potential as a function of temperature. We give upper bounds on the
critical temperature T_c for the onset of superfluidity, obtained by studying
the finite size scaling of the condensate fraction. All of these quantities
were computed for couplings around the unitary regime in the range -0.5 \le
(k_F a)^{-1} \le 0.2, where a is the s-wave scattering length and k_F is the
Fermi momentum of a non-interacting gas at the same density. In all cases our
data is consistent with normal Fermi gas behavior above a characteristic
temperature T_0 > T_c, which depends on the coupling and is obtained by
studying the deviation of the caloric curve from that of a free Fermi gas. For
T_c < T < T_0 we find deviations from normal Fermi gas behavior that can be
attributed to pairing effects. Low temperature results for the energy and the
pairing gap are shown and compared with Green Function Monte Carlo results by
other groups.
