On the dynamics of two photons interacting with a two-qubit coherent feedback network

Abstract

The purpose of this paper is to study the dynamics of a quantum coherent feedback network composed of two two-level systems (qubits) driven by two counter-propagating photons, one in each input channel. The coherent feedback network enhances the nonlinear photon–photon interaction inside the feedback loop. By means of quantum stochastic calculus and the input–output framework, the analytic form of the steady-state output two-photon state is derived. Based on the analytic form, the applications on the Hong–Ou–Mandel (HOM) interferometer and marginally stable single-photon devices using this coherent feedback structure have been demonstrated.