Hanbury Brown–Twiss Photon Antibunching: Single-Photon Purity g²(0)

This simulator reproduces the standard laboratory test used to certify a quantum-dot single-photon source: a Hanbury Brown–Twiss (HBT) interferometer. A triggered photon stream from a simulated quantum dot hits a 50/50 beamsplitter and is time-correlated between two detectors; the live coincidence histogram at zero and non-zero pulse-period delay converges to the second-order correlation g²(τ), whose depth at τ = 0 quantifies single-photon purity. Tune the dot's multi-photon (re-excitation) probability and the detectors' dark-count rate to see antibunching degrade, then engage the heralding time-gate to watch background-driven coincidences fall away faster than genuine detections — the real efficiency-vs-purity trade-off used when heralding a quantum-dot or SPDC single-photon source.