Coupling Between Quantum Dots And Topological Photonic Crystal Cavity

Cavity quantum electrodynamics studies the interaction between cavity photons and quantum emitters.It has been widely proposed for the applications of quantum information processing and optical devices.To study the cavity quantum electrodynamics,both quantum emitters with excellent quantum properties and optical cavities with high quality factor and small mode volume are necessary.Self-assembled quantum dots possess excellent optical properties,outperforming in laser,single photon sources,entangled photon sources and qubits.Photonic crystal cavities have high quality factor and small mode volume,which can greatly enhance the interaction between light and matter.The coupled systems between them can be used to optimize the performance of photonic devices and realize on-chip integrated photonic network.However,the traditional photonic crystal cavities are susceptible to the defects and perturbations,limiting the large-scale applications.The emerging field of topological photonics provides a more robust way to manipulate light.The field exploits the topological ideas to design and control the behavior of light.The topology is related to the global properties of bulk band,and thus possesses the robustness against local defects and perturbations.For example,the topological edge states exhibit unidirectional robust transport,which have been demonstrated to be more robust in applications of unidirectional waveguide,laser and chiral quantum interface.However,the applications of topological photonics are still focused on the topological edge states,and there are few researches on topological cavities.In the paper,we investigate the coupling between topological photonic crystal cavities and quantum dots.The main results are as follows:1.We have designed and fabricated topological cavity with high quality factor and small mode volume.Based on the 2D Su-Schrieffer-Heeger(SSH)model,we designed the second-order topological photonic crystal and trivial photonic crystal.According to the bulk-edge-corner correspondence,there exist 0D topological corner state and 1D edge states at the boundary of the two photonic crystals.The corner state has low mode volume,which can be served as the topological cavity mode.The quality factor of corner state is further optimized by tuning the gap between the two photonic crystals.We fabricated the topological cavity into Ga As slab embedded with quantum dots.Then the optical properties of the topological cavity were studied,laying a foundation for further study on the interaction between topological corner state and quantum dots.2.We demonstrated the Purcell enhancement of single quantum dot due to the topological corner state.In the topological cavity with low density of quantum dots,we studied the interaction between single quantum dot and the topological cavity.The enhancement of photoluminescence intensity and spontaneous emission rate of quantum dot are observed when on resonance with corner state,demonstrating the weak coupling between quantum dots and the topological cavity.Our results show that the topological cavity has wide potential applications in cavity quantum electrodynamics.And this coupling system can be used to optimize the performance of optical devices,such as low-threshold laser,efficient single photon source,etc.3.We experimentally demonstrated a high-performance topological laser based on the corner state.In the cavity with high density of quantum dots,we realized a topological laser based on corner state with high efficiency and low threshold.The threshold is about 1 μW,which is approximately three orders of magnitude lower than those of the current topological edge lasers.The realization of the topological laser downscales the application of topological photonics to nanoscale and demonstrates the great potential of topological cavity on applications in topological nanophotonic devices.4.Based on the above work,the optimization and robustness of topological corner states are further studied experimentally and theoretically.In addition to changing the gap between the two photonic crystal structures,we can also optimize the quality factor by adjusting the position and size of the nearest-neighbor airholes around corner.Moreover,the surface passivation treatment can further optimize the experimental results and obtain a higher quality factor up to 6000.We also systematically studied the robustness of topological corner state against bulk,edge and corner defects.This result paves a way for further applications of topological corner state.5.We proposed a topological cavity based on the slow-light topological edge modes for broadband Purcell enhancement.At the bearded interface between two topologically distinct valley photonic crystals,there exist slow-light topological edge modes with high group index up to 106,featuring the larger Purcell factor.In the topological cavity with bearded interface,we observed very dense cavity modes with high quality factor in a very wide spectral range from both theoretical and experimental results.We demonstrate that the cavity enables the broadband Purcell enhancement together with substantial Purcell factor,having great advantages for the realization of high-efficiency quantum-dot-based single-photon sources and entangled-photon sources.Furthermore,by integrating the topological cavity with the topological waveguide,the chiral transport of single quantum dot can be realized,demonstrating the potential applications in on-chip integrated optical networks.