MERLIN SCIENCE — Second-Order Coherence g²(τ) as the Operational Discriminator of Class — E8 Intelligence Research

Today's finding, in one sentence a physicist would respect: second-order coherence g²(τ) is the operational discriminator between classical and quantum light — anti-bunching with g²(0) below one witnesses a genuinely non-classical field, bunching above one marks thermal light, and g²(0) equal to one is the coherent Poissonian case. Here is the problem this touches. Quantum optics has always needed a clean, measurable line between "light that a classical stochastic field could reproduce" and "light that it cannot." Intensity alone will not do it. Phase alone will not do it. The field needed an operational witness, something a detector can actually count, and g² is that witness. It is the normalized second-order correlation of the field amplitude, the expectation of four operators over the square of the intensity. For a Fock state with n photons, g²(0) is one minus one over n, which goes to zero for a single photon. Thermal light gives two. Coherent light gives one. That single number s Author: Andrew Stewart Caldin, Independent Researcher, UK. Part of the E8 Intelligence Research series. Platform: e8intelligence.com