Cascade Enhancement and Efficient Collection ofSingle Photon Emission under Topological Protection

Topological photonics with the properties of topological robustness and anti-backscattering, brings new strategies for the design of high- performance quantum photonic devices. However, the Purcell factor of quantum emitters in topological photonic crystal structures is relatively small, limiting its application in efficient quantum information processing. Here we demonstrate that both cascade enhancement of magnetic dipole emission and efficient collection of emitted photons can be realized simultaneously in a hybrid structure of a two-dimensional honeycomb topological photonic crystal containing dielectric nanodisk. If a magnetic emitter is used to excite the nanodisk, then its magnetic dipole resonance can be viewed as a large equivalent dipole interacting with the edge states, which achieves the cascade enhancement of the magnetic emitter. In addition, almost all the scattered photons around the nanodisk can be collected through topological edge state with the collection efficiency up to 95%. The proposed mechanism may provide the practical applications of on-chip robust single photon sources and nanolasers.