# Photon propagation through linearly active dimers

## TL;DR

This paper derives an analytic propagator for non-Hermitian dimers with linear gain or loss, analyzing quantum state propagation and potential applications in quantum photonics.

## Contribution

It provides an explicit analytic propagator for non-Hermitian dimers in the quantum regime, including feasible experimental configurations and their quantum state evolution.

## Key findings

- Characterizes mean photon number and correlations for various quantum states
- Identifies signatures for photon switching and entangled source applications
- Analyzes propagation of vacuum, single, and two-photon states

## 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.