A single photon can exist in two different kinds of entanglement at once, and this project will use that property to build a teleportation gate for quantum key distribution. Quantum computers promise to solve problems that are impossible for classical machines, but photonic versions—which use particles of light as qubits—struggle to scale up. The core problem is that standard quantum logic gates become unreliable as more qubits are added. This project tackles that by exploiting "hyper-entanglement," where photons are entangled in both their polarisation and their spatial path simultaneously. The team at the University of York will generate these states using spontaneous parametric down-conversion, then build and test a controlled-NOT gate that uses hyper-entanglement to perform multi-qubit operations more efficiently. If successful, the work would demonstrate a practical route to scalable photonic quantum computers. The immediate impact would be on secure communications: a reliable teleportation gate is a key component for quantum key distribution networks, which protect data from eavesdropping. Longer term, the same architecture could underpin fault-tolerant quantum processors and quantum repeaters for long-distance networking. This is fundamental science—there is no commercial partner or immediate product—but the ability to manipulate multiple degrees of freedom in a single photon could eventually reshape how information is transmitted and processed.
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Quantum computing has the potential to revolutionise computational capabilities by addressing problems intractable for classical systems. Among various quantum computing platforms, photonic quantum computation offers significant advantages due to its resilience to decoherence and rapid gate operation. However, scalability remains a critical challenge. This project investigates the exploitation of hyper-entanglement - entanglement across multiple degrees of freedom (DoF) - to enhance photonic quantum computation, particularly in multi-qubit logic operations. The primary objectives are: (1) Investigate and characterise hyper-entanglement generation using spontaneous parametric down-conversion (SPDC) in the University of York's YCQT labs, ensuring high-fidelity entanglement across multiple DoFs (e.g., polarisation and spatial mode). (2) Develop and implement quantum logic gates, such as the controlled-NOT (CNOT) gate, leveraging hyper-entanglement for multi-qubit operations. (3) Theoretically model these systems using quantum optics formalism and numerical simulations, comparing performance with experimental results. (4) Assess feasibility and scalability, identifying limitations due to decoherence and potential error mitigation strategies. The methodology integrates experimental and theoretical approaches. Experimentally, the project will characterise hyper-entanglement from SPDC sources, implementing quantum gates using linear optical elements and single-photon detectors, with a focus on optical fibre-based setups. Theoretically, quantum gate models will be developed and simulated using numerical techniques such as exact diagonalisation, incorporating decoherence effects. Experimental data will be analysed and optimised based on these models. This research aligns with EPSRC's quantum technologies strategy, specifically within quantum information processing and quantum optics. The findings are expected to contribute to fundamental advancements in scalable photonic quantum computation, with potential implications for secure communications, quantum networking, and fault-tolerant quantum architectures. It does not involve any companies or external collaborators at the moment.
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