Cooling molecular vibrations with shaped laser pulses: Optimal control theory exploiting the timescale separation between coherent excitation and spontaneous emission

摘要

Laser cooling of molecules employing broadband optical pumping involves atimescale separation between laser excitation and spontaneous emission. Here,we optimize the optical pumping step using shaped laser pulses. We derive twooptimization functionals to drive population into those excited state levelsthat have the largest spontaneous emission rates to the target state. We showthat, when using optimal control, laser cooling of molecules works even if theFranck-Condon map governing the transitions is preferential to heating ratherthan cooling. Our optimization functional is also applicable to the lasercooling of other degrees of freedom provided the cooling cycle consists ofcoherent excitation and dissipative deexcitation steps whose timescales areseparated.