New experiments in high-dimensional quantum photonics

Abstract

Quantum computation and quantum communication are on the cusp of moving from theoretical concepts to practical applications, yet the robust generation, manipulation, and detection of photonic quantum states still remains challenging. This thesis introduces experimental techniques in high-dimensional quantum photonics to overcome these hurdles and pave the way for future quantum technologies. To address the generation challenge, we look at high-dimensional entanglement as a way to increase both information capacity and noise resilience of quantum channels. A novel indicator of entanglement, the quantum contrast (Q), is introduced to quantify the amount of quantum correlations in an entangled state. By studying Q under varying noisy conditions through theoretical, numerical, and experimental approaches, we demonstrate that, in specific cases, increasing the dimensionality enhances the robustness of entanglement - a critical factor for secure quantum communication and efficient quantum networks. On the manipulation front, we develop a multi-plane light converter (MPLC) using a spatial light modulator (SLM) to perform complex unitary transformations on spatial modes of light. This device is used to execute unambiguous state discrimination (USD) of non-orthogonal states, a measurement strategy that guarantees error-free identification of the original state at the cost of occasional inconclusive outcomes. The same MPLC setup achieves a 97.6% accuracy in a classical image classification task, showing its versatility and potential for both quantum measurements and classical optical processing. Together, these experiments offer key insights into the fundamental behaviour of high-dimensional quantum states and their practical manipulation. By bridging the gap between theoretical predictions and experimental implementations, this work advances our understanding of noise resilience in entangled systems and introduces robust methods for high-fidelity state discrimination. The developments presented here are critical steps toward realising secure, high-capacity quantum communication networks and scalable quantum computing platforms in real-world settings.