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.