Quantum dynamics of a millikelvin quasibound KRb complex in a low-frequency field

We investigate computationally the quantum dynamics of a metastable K-40 Rb-87 complex in the ground electronic state (X-1 Sigma(+)) under an intense continuous-wave low-frequency field. We focus on an initial condition where the atoms are quasibound in an orbiting resonance with an energy that corresponds to a kinetic temperature of 62 mK and with a lifetime of 3 ns. A microwave field is tuned either to another lower-lying orbiting resonance or to a high-lying bound vibrational level. In both cases, we observe a transient photoacceleration of the half-collision. However, the photodissociation of the complex is suppressed by strong quasibound-free Rabi oscillations, although it still dissociates nonradiatively with the lifetime of the initial orbiting resonance. During the transient period, a sizable multiphoton association in high-lying vibrational levels is achieved, accompanied by a development of a wide rotational distribution. Therefore, this mechanism seems promising as the basis of a general strategy for the controlled formation of diatomic molecules from gases at millikelvin temperatures.