1 Answers
Cavity quantum electrodynamics 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 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 | e ⟩ | n − 1 ⟩ ↔ | g ⟩ | n ⟩ {\displaystyle |e\rangle |n-1\rangle \leftrightarrow |g\rangle |n\rangle } , that is between an excited atom and n − 1 {\displaystyle n-1} photons, and a ground state atom and n {\displaystyle 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, | 0 ⟩ ↔ | g ⟩ {\displaystyle |0\rangle \leftrightarrow |g\rangle } , and can be repeated to swap it back again; this could be used as a single photon source , or as an interface between an atom or trapped ion quantum computer and optical quantum communication.
Other interaction durations create entanglement between the atom and cavity field; for example, a quarter-cycle on resonance starting from | e ⟩ | 0 ⟩ {\displaystyle |e\rangle |0\rangle } gives the maximally entangled state / 2 {\displaystyle /{\sqrt {2}}}. This can in principle be used as a quantum computer, mathematically equivalent to a trapped ion quantum computer with cavity photons replacing phonons.