Photonic Nanostructures for Efficient Coupling and Light Enhancement in Semiconductor Quantum Technologies

This work presents innovative photonic nanostructures for semiconductor quantum dots, which are promising candidates for quantum technologies such as quantum cryptography and quantum computation. Through these nano structures their brightness and coupling efficiency is improved beyond existing devices. First, grating couplers for fiber-to-chip coupling on a III-V semiconductor platform are presented. Furthermore, a stable fiber-to-chip coupling method is demonstrated that can inject telecom C-band single photons into a SOI photonic chip by combining high-efficiency grating couplers and angle-polished single-mode fibers. In addition, photonic nanostructures based on ridge waveguides are designed and fabricated to be compatible with Stranski-Krastanov grown InAs and droplet-etched GaAs quantum dots, a critical step towards fully integrated photonic integrated circuits. This work culminates in the first demonstration of circular Bragg grating cavities operating in the telecom O-band and C-band with unprecedented single-photon brightness and Purcell enhancement, laying the foundation for highly efficient and advanced quantum information processing devices.