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. gives the maximally entangled state (a Bell state)