Second order optical nonlinear processes as tools to probe anomalies inside high confinement microcavities

Abstract

The interest toward strong electromagnetic confinement structures through the use of microcavities is of great interest, from both the fundamental understanding and the technological application sides. Here, we focus our attention to second order nonlinear processes inside such structures. From a basic point of view, electromagnetic confinement leads, physically, to the manipulation of vacuum field fluctuations and, formally, to an anomalous commutation relation [Ueda, M. and Imoto, N., "Anomalous commutation relation and modified spontanenous emission inside a microcavity," Phys. Rev. A, 50(1), 89-92 (1994)]. However, an attempt to probe the resulting anomaly with a beam splitter located inside a cavity is theoretically proved inadequate for this task. For this reason, parametric fluorescence (PF, parametric down conversion) and second harmonic generation (SHG) are considered as potential tools to probe vacuum field fluctuations in confinement structures. Indeed, it was recently showed that PF can be strongly intensified, by two orders of magnitude or more, when it occurs inside a high confinement (open) cavity. Therefore, PF could efficiently be used to probe the expected anomaly. Additionally, in consideration of the simplest possible experimental scheme to probe the anomaly and because it is generally admitted that SHG is the time reversal of degenerate parametric fluorescence, here our attention is also directed toward SHG. Formally, we show that the equations describing SHG and PF are not symmetrical regarding quantum noise. It turns out that, conversely to the case of PF, the intensification of vacuum field fluctuations tends to inhibit SHG. We interpret this result as due to the reduction of waves coherence induced by stronger quantum noise. In conclusion, albeit both processes could be used as probes to prove or disprove the realm of quantum anomalies, PF appears as a more convenient tool.