  The efficiency of converting two-species fermionic atoms into bosonic
molecules is investigated in terms of mean-field Lagrangian density. We find
that the STIRAP technique aided by Feshbach resonance is more effective than
the bare Fechbach resonance for $^6$Li atoms rather than $^{40}$K atoms. We
also make general consideration on the symmetry and its relevant conservation
law, which enable us to introduce a natural definition of adiabatic fidelity
for CPT state. The calculated values of the fidelity then provide an
interpretation on why the conversion efficiencies for $^{40}$K and $^6$Li are
distinctly different.
