Frustrated Two-Photon Creation in a Time-Dependent Cavity

In the process of parametric downconversion, a high-energy photon is annihilated to create a pair of lower-energy photons within a nonlinear dielectric material. It was shown some years ago that this process can be modified by quantum interference, by reflecting the high-energy and low-energy light back into the dielectric. The suppression or enhancement of the downconversion rate is analogous to the phenomenon of inhibited spontaneous emission that occurs when an excited atom is placed in a cavity whose allowed modes cannot Support the spontaneous emission. In this case, the atom remains excited - but then, how does it interact with the cavity? If the cavity mirror were replaced by a detector, could photons be counted immediately, or only after some time delay? Our experiment uses spontaneous downconversion, a 2-m long cavity, and a fast optical switch to obtain the answer.