Unidirectional propagation of single photons realized by a scatterer coupled to whispering-gallery-mode microresonators

Coherently manipulating single photons in nanophotonic structures with unidirectional propagation is one of the central goals for integrated quantum information processing. Photonic devices constructed by a single atom coupled to a whispering-gallery-mode microresonator (WGMM) with nonideal chiral photon-atom interactions inevitably induce undesired photon scattering. Here, an external scatterer is introduced to the WGMM to cancel the reflection of signal photons by an atom due to nonideal chiral interactions. By properly tuning the positions of the scatterer, destructive and constructive interferences between reflected photons of different pathways are utilized to control the reflection properties of single incident photons. The results show that the reflection prob-abilities can be suppressed by applying the interplay between chirality and backscattering. Constructing perfect destructive interferences directly leads to unidirectional propagation even when the photon-atom interactions are not ideal. Because the amplitudes of the reflected photons produced by the scatterer can be enhanced to meet requirements of perfect destructive interfering processes, unidirectional propagation is preserved against dissipations.

Automated summary

Manipulating single photons coherently and achieving unidirectional propagation are important goals for integrated quantum information processing. In this study, an external scatterer is introduced to cancel the reflection of photons caused by nonideal chiral interactions in a photonic device. By controlling the interference between reflected photons, the reflection properties of single incident photons can be controlled, leading to unidirectional propagation even with nonideal photon-atom interactions.