The physical origin of a photon-number parity effect in cavity quantum electrodynamics

The rapidly increasing capability to modulate the physicochemical properties of atomic groups and molecules by means of their coupling to radiation, as well as the revolutionary potential of quantum computing for materials simulation and prediction, fuel the interest for non-classical phenomena produced by atom-radiation interaction in confined space. One of such phenomena is a “parity effect” that arises in the dynamics of an atom coupled to two degenerate cavity field modes by two-photon processes and manifests itself as a strong dependence of the field dynamics on the parity of the initial number of photons. Here we identify the physical origin of this effect in the quantum correlations that produce entanglement among the system components, explaining why the system evolution depends critically on the parity of the total number of photons. Understanding the physical underpinnings of the effect also allows us to characterize it within the framework of quantum information theory and to generalize it. Since a single photon addition/removal has dramatic effects on the system behavior, this effect may be usefully applied, also for amplification purposes, to optoelectronics and quantum information processing.