Chiral Single-Photon Interface:Isolation And Unidirectional Emission

The photonic chips for quantum information processing can achieve high precision and universal quantum control and quantum measurement of opti-cal quantum systems,which are one of the keys to the current quantum tech-nology revolution.At present,scientific research urgently needs to expand the functionality of integrated quantum optical components and enhance its ability to process quantum information,thereby promoting the application of quantum information technology.Chiral quantum optics is a new research field developed in recent years.It mainly studies the process of chiral coupling of light and quantum emitters in nanostructures.For example,the field transversely confined in nano-optical waveguides or nano-optical fibers produces a longitudinal electric field component along the direction of propagation,exhibiting a distribu-tion of locally circularly polarized electric fields,and the polarization of the electric fields depending on the direction of propagation,which is called op-tical chirality.At the particular location in these structures,the coupling strength of the quantum emitter to the chiral electric field is also depending on the direction of light propagation.Based on chiral quantum optics and cavity quantum electrodynamics,this paper designs a multi-functional on-chip chiral interface,which can manipulate single photon information,and achieve single photon isolation and unidirectional photon emission.This paper mainly includes:i.We build the chiral single photon interface,which is a chiral coupling system consisting of a waveguide,a microring resonator,and a quantum dot.Using electromagnetic simulation methods,we designed a microring resonator with chiral circularly polarized electric field distributions.When the photon is incident in the positive direction,the evanescent field nearby the outside wall of the resonator is near perfect left-handed circularly polarized light,and when the photon is incident in the opposite direction,the evanescent field at the same position is a near perfect right-han ded circlarly polarized light.ii.We show a broadband optical isolation at the single-photon level over several gigahertz.The quantum dot is placed nearby the outside wall of the resonator and initialized to couple only with the left-hand circularly polarized light.Therefore,since the coupling strength between the light and the quantum dot in different propagation directions is inconsistent,single photon isolation is realized.iii.We show unidirectional and polarization-deterministic single-photon emis-sion.When the quantum dot is initially prepared in its excited state,it will emit a single photon into either the CW mode or the CCW one in the strong-couping regime.The exiting path of the photon is determined by the populated excited state of the QD.Therefore,by initializing the QD in a spin-selective excited state,we can realize the unidirectional emission of single photons.And the emitted photon can be a long-pulsed single photon or a time-bin single photon.