Single-Photon Source — Antibunching Simulator

Light source

Pump rate 4 Hz

Mean photons / pulse (μ) 0.55

Live statistics

Pulses fired

Coincidences

Detector A

Detector B

g²(0) — coincidence probability at zero delay

–

A single photon can only go one way at the beamsplitter — detectors almost never click together. Watch the centre bar of the histogram stay near zero.

How it works

Every pump pulse either excites the quantum dot or, in laser mode, attenuates a weak coherent pulse. The emitted light hits a 50/50 beamsplitter and is routed to Detector A or Detector B. A running cross-correlation of the two detector click-records builds the g²(τ) histogram, in units of the pulse period τ.

g²(τ) = ⟨n_A(t)·n_B(t+τ)⟩ / (⟨n_A⟩⟨n_B⟩)

Quantum dot — each excitation stores at most one electron-hole pair, so at most one photon can ever leave per pulse. It can never split to both detectors at once, so g²(0) is pinned near 0: perfect antibunching.
Attenuated laser — a coherent (Poissonian) source occasionally emits 2 or more photons in the same pulse purely by chance, so both detectors sometimes click together. g²(0) stays near 1, exactly like all the side peaks.
Pump rate — how often pulses arrive; only changes animation speed, not the statistics.
Mean photons / pulse (μ) — sets the average brightness for both sources so the comparison is fair; quantum-dot excitation probability is capped at 1 photon regardless of μ.

Real-world relevance: this Hanbury Brown–Twiss measurement is the standard lab test used to certify quantum-dot, colour-centre and molecule-based single-photon sources for quantum key distribution and photonic quantum computing — a device only counts as a genuine single-photon source if its measured g²(0) drops well below 0.5.

Pump pulse Emitted photon Detector click

⚠ Couldn't load the 3D engineThree.js failed to load from the CDN. Check your connection and reload.

g²(τ) coincidence histogramQuantum dot