Unidirectional interaction between quantum emitters coupled to a plasmonic waveguide.

Surface plasmon polaritons (SPPs) confined at a metal-dielectric interface exhibit spin-orbit interaction, a fundamental mechanism in chiral quantum optics that provides an additional degree of freedom to control light-matter interaction. For fabricating directional quantum devices, establishing a unidirectional interaction between quantum emitters (QEs) is essential. In this work, we theoretically investigate the SPP-mediated interaction between chiral QEs coupled to a one-dimensional plasmonic waveguide, using a macroscopic quantum electrodynamic approach. Our analytic result for the interaction reveals its nonreciprocal character. We demonstrate that a unidirectional interaction between QEs can be achieved by balancing the coherent and dissipative interactions. Moreover, we study the resulting quantum-optical properties of the system, observing enhanced quantum correlations and modified resonance fluorescence from the QEs. Our findings advance the understanding of light-matter interaction in quantum plasmonics and support the development of directional quantum devices at the nanoscale.