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

TL;DR

This paper analyzes how a quantum feedback network with two qubits influences two-photon interactions, deriving steady-state outputs and demonstrating applications in quantum interferometry and photon devices.

Contribution

It provides an analytic derivation of the steady-state two-photon output state in a feedback network with two qubits, highlighting enhanced nonlinear interactions.

Findings

Enhanced photon-photon interaction within the feedback loop

Analytic form of the steady-state two-photon output derived

Applications demonstrated in HOM interferometry and single-photon devices

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. The difference between continuous-mode and single-mode few-photon states is demonstrated.