  We discuss fast frictionless cooling techniques in the framework of
sympathetic cooling of cold atomic mixtures. It is argued that optimal cooling
of an atomic species - in which the deepest quantum degeneracy regime is
achieved - may be obtained by means of sympathetic cooling with another species
whose trapping frequency is dynamically changed to maintain constancy of the
Lewis-Riesenfeld adiabatic invariant. Advantages and limitations of this
cooling strategy are discussed, with particular regard to the possibility of
cooling Fermi gases to a deeper degenerate regime.
