Two-Photon Gateway in One-Atom Cavity Quantum Electrodynamics

TLDR

Single atoms absorb and emit light from a resonant laser beam photon by photon. The authors demonstrate that a single atom strongly coupled to an optical cavity can absorb and emit resonant photons in pairs, observed via photon‑correlation measurements, and suggest this could enable controlled two‑photon interactions. This pairwise photon absorption and emission arises from the quantum anharmonicity of the atom‑cavity energy structure. The atom‑cavity system converts a random input photon stream into a correlated output stream, functioning as a two‑photon gateway.

Abstract

Single atoms absorb and emit light from a resonant laser beam photon by photon. We show that a single atom strongly coupled to an optical cavity can absorb and emit resonant photons in pairs. The effect is observed in a photon correlation experiment on the light transmitted through the cavity. We find that the atom-cavity system transforms a random stream of input photons into a correlated stream of output photons, thereby acting as a two-photon gateway. The phenomenon has its origin in the quantum anharmonicity of the energy structure of the atom-cavity system. Future applications could include the controlled interaction of two photons by means of one atom.