Fig. 1: Different case scenarios in two-photon interferometry using a MZ-type device.
From: Quantum-limited determination of refractive index difference by means of entanglement
a The pair can travel along four different paths. Interference in the coincidence counts can occur provided two paths are indistinguishable. Note that the different colors for the two photons are for representation purpose only. Ideally the paired photons are indistinguishable. b Interference pattern at the output of a balanced interferometer.
