Single‑photon Source

A single‑photon source is a device engineered to emit light in such a way that each excitation of the source releases exactly one photon, with negligible probability of emitting zero or more than one. Unlike ordinary lamps or lasers, which produce streams of many photons obeying Poisson statistics, a true single‑photon emitter exhibits antibunching: successive detection events are spaced farther apart than any classical light field would allow. Realizations range from isolated atoms and ions trapped in vacuum to solid‑state defects such as nitrogen‑vacancy centers in diamond or semiconductor quantum dots coupled to optical cavities.

The importance of single‑photon sources lies in their role as the fundamental information carriers for photonic quantum technologies. Quantum key distribution, entanglement swapping, linear‑optical quantum computing, and certain precision measurement schemes require that each logical qubit be represented by a distinct photon whose quantum state is well defined and controllable. Any multi‑photon contamination introduces errors that quickly degrade security or computational fidelity, making deterministic or highly pure single‑photon emission a key performance metric.

You will encounter single‑photon sources wherever individual photons are deliberately harnessed: in laboratory demonstrations of quantum teleportation, in fiber‑based QKD networks linking distant users, inside integrated photonic chips that implement gate operations via interference, and increasingly in emerging commercial devices such as quantum random number generators. Their design continues to evolve toward higher extraction efficiency, on‑demand timing, indistinguishability across separate sources, and compatibility with scalable manufacturing processes.