Cavity quantum electrodynamics
Cavity quantum electrodynamics (cavity QED) is the study of the interaction between light confined in a reflective cavity and atoms or other particles, under conditions where the quantum nature of light photons is significant. It could in principle be used to construct a quantum computer.
The case of a single 2-level atom in the cavity is mathematically described by the Jaynes-Cummings model, and undergoes vacuum Rabi oscillations , that is between an excited atom and n-1 photons, and a ground state atom and n photons.
If the cavity is in resonance with the atomic transition, a half-cycle of oscillation starting with no photons coherently swaps the atom qubit's state onto the cavity field's, , and can be repeated to swap it back again; this could be used as a single photon source (starting with an excited atom), or as an interface between an atom or trapped ion quantum computer and optical quantum communication.
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