Physics / mechanism
A single-photon source (SPS) emits exactly one photon per excitation cycle—verified by sub-Poissonian statistics and Hanbury Brown–Twiss g²(0) < 0.5 (ideal: 0). Key platforms: nitrogen-vacancy (NV) and silicon-vacancy (SiV) centres in diamond, self-assembled InGaAs quantum dots (QDs), hexagonal boron nitride (hBN) defects, and parametric downconversion sources. Performance metrics: single-photon purity (g²(0)), indistinguishability (Hong-Ou-Mandel visibility >99% demonstrated for InGaAs QDs at ~1 GHz clock rates), brightness (>10 MHz detected photons/s), and operating temperature (QDs typically 4–10 K; hBN room-temperature capable). Telecom-band emission (1310/1550 nm) is the integration bottleneck for fibre-compatible deployment.
Competitive landscape
InGaAs QDs in photonic crystal cavities dominate indistinguishability benchmarks but require cryogenics. Diamond colour centres offer longer coherence but low brightness without nanophotonic enhancement. hBN trades indistinguishability for room-temperature operation. Parametric sources are probabilistic—scalable but lossy. Atomic vapours (Rb, Cs) and trapped ions compete for lab-grade purity.
Companies using
Connected ideas
Sources
Frontier (open questions)
- To be added.