Nonlinear Integrated Photonics for Quantum State Generation and Processing

Abstract

Photons are natural carriers of quantum information that have played a central role in understanding quantum physics and a wide range of photonic quantum technologies.
Today, the realisation of a photonic quantum computer poses a vast technological challenge in terms of the scale and performance of devices required in broadly three key aspects: the generation, processing, and detection of quantum states of light.
Integrated photonics is playing a central role in addressing these challenges as a highly manufacturable and scalable technology, able to perform tasks with ever increasing levels of performance in compact devices.
However, continued innovation of devices is required to meet stringent requirements in the most effective and resource efficient way.

To this end, in this thesis we focus on the generation and processing of photonic states using nonlinear effects in integrated photonic platforms.
We characterise a source optimised for the generation of spectrally pure single-mode squeezed vacuum based on microring resonators with (97.875±0.001)% purity and demonstrate >15 dB of suppression of parasitic nonlinear processes that otherwise introduce loss and noise.
For manipulating photonic states, we investigate using cross-phase modulation as a fast, all-optical switching mechanism using a mid-infrared pump for the enhanced nonlinear optical properties of silicon at wavelengths beyond the telecommunications bands.
We observe phase shifts of (0.087±0.002)π on picosecond timescales and gain insights into reaching π phase shifts in future devices.
Finally, we use a quantum dot as a light-matter interface to perform multimode nonlinear operations at the few-photon level through integration into a photonic circuit.
We demonstrate programmability over both linear operations and nonlinear photon-scattering operations, going beyond what is possible with linear optics alone.

These works offer insights into the development of squeezed light sources, all-optical switches, and the introduction of light-matter interfaces into photonic circuits to unlock novel functionality for scalable quantum photonic technologies.

Date of Award	9 Dec 2025
Original language	English
Awarding Institution	University of Bristol
Supervisor	Anthony Laing (Supervisor) & Alex S Clark (Supervisor)