Partial distinguishability and photon counting probabilities in linear multiport devices

Abstract

Probabilities of photon counts at the output of a multiport optical device are generalised for optical sources of arbitrary quantum states in partially distinguishable optical modes. For the single-mode photon sources, the generating function for the probabilities is a linear combination of the matrix permanents of positive semi-definite Hermitian matrices, where each Hermitian matrix is a Hadamard product of a submatrix of the multiport matrix and a Hermitian matrix describing partial distinguishability. For the multi-mode sources the generating function is given by an integral of the Husimi functions of the sources. When each photon source outputs exactly a Fock state, the obtained expression reduces to the probability formula derived for partially distinguishable photons, \textit{Physical Review A \textbf{91}, 013844 (2015)}. The derived probability formula can be useful in analysing experiments with partially distinguishable sources and error bounds of experimental Boson Sampling devices.