Figure 2From: Enhanced Hanbury Brown and Twiss interferometry using parametric amplificationSchematic diagram of an ideal OPA. It consists of a pump beam and two input modes denoted by annihilation operators, \(\hat{a}_{\text{in}}\) and \(\hat{b}_{\text{in}}\), incident on the OPA. The \(\hat{a}_{\text{out}}\) and \(\hat{b}_{\text{out}}\) are the two output modesBack to article page