  We consider an ideal gas of Bose and Fermi atoms in a harmonic trap, with a
Feshbach resonance in the interspecies atomic scattering that can lead to
formation of fermionic molecules. We map out the phase diagram for this
three-component mixture in chemical and thermal equilibrium. Considering
adiabatic association and dissociation of the molecules, we identify a possible
cooling cycle, which in ideal circumstances can yield an exponential increase
of the phase-space density.
