Nonreciprocal single-photon band structure

TL;DR

This paper explores nonreciprocal single-photon band structures in a 1D coupled-resonator waveguide with chiral quantum emitter interactions, enabling high-fidelity quantum circulators and protected photon propagation.

Contribution

It introduces a novel chiral QE-CROW system that breaks time-reversal symmetry, creating nonreciprocal band features and enabling quantum photonic devices with enhanced control.

Findings

Nonreciprocal edge states and flat bands appear due to chiral coupling.

High-fidelity, low-loss single-photon circulators are achieved.

One-way photon propagation is protected against backscattering.

Abstract

We study single-photon band structure in a one-dimensional (1D) coupled-resonator optical waveguide (CROW) which chirally couples to an array of two-level quantum emitters (QEs). The chiral interaction between the resonator mode and the QE can break the time-reversal symmetry without the magneto-optical effect. As a result, a nonreciprocal single-photon edge state, band gap and flat band appear. By using such a chiral QE-CROW system, including a finite number of unit cells and working in the nonreciprocal band gap, we achieve frequency-multiplex single-photon circulators with high fidelity and low insertion loss. The chiral QE-light interaction can also protect one-way propagation of single photons against backscattering. Our work opens a new door for studying nonreciprocal photonic band structure and exploring its applications in the quantum regime.