Intensity correlations in the Wigner representation

We derive a compact expression for the second-order correlation function g⁽²⁾(0) of a quantum state in terms of its Wigner function, thereby establishing a direct link between g⁽²⁾(0) and the state’s shape in phase space. We conduct an experiment that simultaneously measures g⁽²⁾(0) through direct photocounting and reconstructs the Wigner function via homodyne tomography. The results confirm our theoretical predictions. This article is part of the theme issue ‘The quantum theory of light’.