Multiphoton quantum interference on a dipole-forbidden transition

We investigate the effect of an intense low-frequency field on the population decay of an excited two-level atom, where the two states are connected by a dipole-forbidden transition. In addition to the natural two-photon spontaneous decay, the low-frequency field gives rise to induced two-photon processes, where one of the two photons is spontaneous. Due to the low frequency of the applied field, the induced decay pathways may interfere with each other. We show how varying the parameters of the applied field allows switching between constructive and destructive interference, thereby increasing or decreasing the induced transition rate as compared to the rate without interference. As all relevant competing transitions are of the same multiphoton order, the system is a promising candidate to verify the idea of spontaneous-emission interference induced by multiphoton pathways experimentally