  The Fermi gas at unitarity is a particularly interesting system of cold
atoms, being dilute and strongly interacting at the same time. It can be
studied non-perturbatively with Monte Carlo methods, like the recently
developed worm algorithm. We discuss our implementation and tests of this
algorithm and suggest a modification that increases its efficiency by reducing
autocorrelations. We then show how the worm algorithm can be applied to
calculate the critical temperature of an imbalanced Fermi gas (unequal number
of fermions in the two spin components). We finally present some results
obtained with the modified algorithm, in the balanced as well as in the
imbalanced case.
