Studies on performance improvement of semiconductor-based quantum emitters using quasi-resonant optical excitation and circular Bragg grating

Abstract

Quantum light sources are essential elements in various fields of quantum information science, such as quantum communication, quantum computation, and quantum metrology. Although various platforms are being studied to realize quantum emitters, semiconductor quantum dots (QDs) offer advantages in terms of ease of integration with optical and electrical devices, as well as scalability. However, semiconductor QDs suffer from drawbacks, including reduction of single-photon purity due to emission from the surrounding semiconductor materials and degraded coherence properties caused by fluctuation in the electric field around the quantum dots. Additionally, the random direction of emission of QDs limits the amount of light captured to the limited numerical aperture. In this thesis, we demonstrated that polarization-controlled quasi-resonant excitation can enhance the single-photon purity and coherence properties of semiconductor QDs. Furthermore, by combining QDs with a circular Bragg grating, we increased the collection efficiency of light in a limited numerical aperture and observed an increase in the spontaneous emission rate. Also, we developed the nanoscale focus pinspot method to enhance the single-photon purity of QDs without the reduction of QD signal intensity and destruction of neighboring photonic structures. We anticipate that these research findings can be applied to various quantum emitters based on other semiconductor-based QDs and defects in solids, thereby enhancing the performance of quantum emitters.