Concept 11 of 42 · Quantum Light and Emitters

Second-order coherence

Photon correlations reveal bunching, antibunching and nonclassical emission.

01 / Mathematical framework

$$g^{(2)}(0)=\frac{\langle a^\dagger a^\dagger aa\rangle}{\langle a^\dagger a\rangle^2}$$

Physical intuition

Photon correlations reveal bunching, antibunching and nonclassical emission. This is the starting point for understanding how nanoscale optical geometry changes the states or dynamics accessible to light and matter.

Deep dive: how the mechanism works

The normalized coincidence rate measures two-photon arrival correlations; ideal single-photon emission yields zero equal-time coincidence.

How the quantum phenomenon appears

A Hanbury Brown–Twiss setup measures antibunching from a quantum dot. To distinguish a genuinely quantum signal from a classical optical response, connect the device physics to a measurement such as photon correlations, interference visibility, energy-level structure or quantum-state tomography where appropriate.

Assumptions and limitations

Detector jitter, background counts and blinking can alter measured values.

Research and simulation exercise

Identify the tunable parameters, predict the observable from the stated model, and sweep one parameter while holding the others fixed. Compare against a simpler reference model, quantify loss and uncertainty, and state which observations would falsify the hypothesis.

Connect the ideas

Fock states and coherent states Two-level quantum emitters

See the chapter guide and further reading.

← Previous Next concept →

λSecond-order coherence