  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 laser-dressed atom-molecule system, we obtain an integro-differential
master equation for the the system's reduced density matrix. The equation is
numerically solved to describe system dynamics in the presence of decay. In
particular, we discuss correlated spontaneous emission from a pair of
electronically excited diatomic ro-vibrational states due to their laser
induced coupling to the ground continuum of atomic scattering states. This
allows us to calculate time-dependence of emitted radiation intensity. It
exhibits quantum beats due to coherent dynamics. 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 from the
molecular excited states and the decoherence between them by changing the
relative intensity and the phase between the 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.
