  We propose a double-well configuration for optical trapping of ultracold
two-species Fermi-Bose atomic mixtures. Two signatures of macroscopic quantum
coherence attributable to a superfluid phase transition for the Fermi gas are
analyzed. The first signature is based upon tunneling of Fermi pairs when the
power of the deconfining laser beam is significantly reduced. The second relies
on the observation of interference fringes in a regime where the fermions are
trapped in two sharply separated minima of the potential. Both signatures rely
on small decoherence times for the Fermi samples, which should be possible by
reaching low temperatures using a Bose gas as a refrigerator, and a bichromatic
optical dipole trap for confinement, with optimal heat-capacity matching
between the two species.
