  A method for creation of ultracold molecules by stepwise adiabatic passage
from the Feshbach state to the fundamentally ground state using an optical
frequency comb is presented within a semiclassical multilevel model. The
sinusoidal modulation of the spectral phase of the comb is implemented that
leads to a creation of a quasi-dark dressed state having an insignificant
population of the excited state manifold and, thus, efficiently mitigating
decoherence in the system. In contrast, the cosine modulation does not lead to
the quasi-dark state formation. The results demonstrate the importance of the
parity of the spectral chirp in quantum control.
