III-V semiconductor photonic devices for scalable quantum architectures

This thesis describes the optimisation of nanophotonic elements for on-chip integration with III-V semiconductor InAs/GaAs quantum dot single-photon sources and the investigation of photon-mediated interactions between pairs of quantum dots in nanophotonic waveguides. Effective coupling of light on/off-chip is important for the study of light-matter interactions in nanophotonic systems and for efficient operation of quantum optical devices, such as single-photon sources. Here, optimisation of a circular grating outcoupler coupled to a nanophotonic waveguide is investigated for efficient on/off-chip light coupling. Broadband light input demonstrates increased transmission into an off-chip optical fibre and reduced reflection back into the waveguide, compared to the previous best design, for the InAs/GaAs quantum dot emission wavelength region of 900-950 nm. On-chip control and routing requires nanophotonic beamsplitters. Two approaches are investigated here. The first is a directional coupler beamsplitter, designed with a wider waveguide separation for better fabrication tolerance, providing even splitting with minimal loss in simulation. The second is a multimode interferometer beamsplitter, designed with two permutations of input/output waveguides, whereby broadband light transmission demonstrates even splitting with minimal loss for both designs. Finally, photon-mediated interactions between pairs of quantum dots in a nanophotonic waveguide are studied. Understanding such interactions is important for nanophotonic systems in which multiple quantum dots interact. The temporal dynamics of a waveguide- embedded quantum dot pair is simulated, demonstrating superradiant and subradiant effects on the coupled quantum dot decay times. Experimentally, quantum dots are resonantly coupled using an applied magnetic field, the photon statistics revealed by Hanbury Brown-Twiss interferometry. For a coupled quantum dot pair in a nanophotonic waveguide, a coherent punching peak is observed, the signature of superradiance.