Fluorescence control through multiple interference mechanisms

We discuss the spontaneous emission from a coherently prepared and microwav e-driven doubler of potentially closely spaced excited states to a common g round level. Multiple interference mechanisms are identified that may lead to fluorescence inhibition in well-separated regions of the spectrum or act jointly in canceling the spontaneous emission. In addition to phase-indepe ndent quantum interferences due to combined absorptions and emissions of dr iving field photons, we distinguish two competing phase-dependent interfere nce mechanisms as means of controlling the fluorescence. The indistinguisha ble quantum paths may involve the spontaneous emission from the same state of the doublet, originating from the two different components of the initia l coherent superposition. Alternatively the paths involve a different spont aneous photon from each of two decaying stares, necessarily with the same p olarization. This makes these photons indistinguishable in principle within the uncertainty of the two decay rates. The phase dependence arises for bo th mechanisms because the interfering paths differ by an unequal number of stimulated absorptions and emissions of the microwave field photons. [S1050 -2947(98)03011-X].