Few-photon isolation in a one-dimensional waveguide using chiral quantum coupling

We investigated the transmission of single and two photons in a one-dimensional waveguide that is coupled with a Kerr micro-ring resonator and a polarized quantum emitter. In both cases, a phase shift occurs, and the non-reciprocal behavior of the system is attributed to the unbalanced coupling between the quantum emitter and the resonator. Our analytical solutions and numerical simulations demonstrate that the nonlinear resonator scattering causes the energy redistribution of the two photons through the bound state. When the system is in the two-photon resonance state, the polarization of the correlated two photons is locked to their propagation direction, leading to non-reciprocity. As a result, our configuration can act as an optical diode.