Molecular cooling via Raman transitions and a harmonic spectral modulation of an optical frequency comb: The role of the parity of the chirp in quantum control

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.