Title: Photon propagation through linearly active dimers,
Abstract: We provide an analytic propagator for non-Hermitian dimers showing linear
gain or losses in the quantum regime. In particular, we focus on experimentally
feasible realizations of the $\mathcal{PT}$-symmetric dimer and provide their
mean photon number and second order two-point correlation. We study the
propagation of vacuum, single photon spatially-separable, and two-photon
spatially-entangled states. We show that each configuration produces a
particular signature that might signal their possible uses as photon switches,
semi-classical intensity-tunable sources, or spatially entangled sources to
mention a few possible applications.