Decay dynamics in a strongly driven atom-molecule coupled system

Within the framework of master equation, we study decay dynamics of an atom-molecule system strongly coupled by two photoassociation lasers. Summing over the infinite number of electromagnetic vacuum modes that are coupled to the system, we obtain an integro-differential master equation for the system's reduced density matrix. We use this equation to describe correlated spontaneous emission from a pair of electronically excited diatomic ro-vibrational states. The temporal evolution of emitted radiation intensity shows quantum beats that result from the laser-induced coherence between the two excited states. The phase difference between the two driving fields is found to significantly affect the decay dynamics and the beats. Our results demonstrate the possibility to control decay and decoherence in the system by tuning the relative intensity and the phase between the two lasers. We further show that if the ground-state continuum has a shape resonance at a low energy, then the quantum beats show two distinctive time scales of oscillations in the strong coupling regime. One of the time scales originates from the energy gap between the two excited states while the other time scale corresponds to the collision energy at which free-bound Franck-Condon overlap is resonantly peaked due to the shape resonance.