Quantum computing and communication with spin-photon interfaces

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This project falls within the ESPRC Quantum Technologies research area. The project focuses on quantum communication technologies, and how nodes in a network can be leveraged to perform quantum information processing tasks. In particular, the work will explore the potential of GaAs quantum dots and more generally central spin systems for quantum memory and quantum computation. Coherent light matter interfaces are the leading candidates for a quantum memory as they can store a qubit in its quantum state, have long coherence times and enable single photon control. The hyperfine interaction between electron spin and nuclear spin ensembles in a quantum dot makes them an excellent host. This project aims to explore the potential of GaAs quantum dots and more generally central spin systems for quantum information by extending theoretical models of the system and control protocols, and numerically simulating the outcome under realistic parameters.Initially the project will focus on the modelling and analysis of a quantum repeater protocol. Quantum repeaters based on quantum memories enable the long-distance transmission of quantum states. A quantum repeater protocol involves making simultaneous bell state measurements on nearby entangled photons to transmit the state over longer distances. Ensuring these measurements are simultaneous becomes harder the longer the distance and so quantum memories are needed to hold the state for the necessary period to make every measurement. In the first year this scheme will be adapted to a central spin system and the qubit coherence, and the fidelity of the qubit storage and retrieval will be determined. Further to this, simulations of the creation of a photonic cluster state scheme in the GaAs quantum dots will be developed. Single photon systems suffer greatly from loss affecting the fidelity of a system and the generation of a cluster state means that information is shared, and the system is robust against the loss of a few photons. The creation of a cluster in diamond colour centres has already been researched, and in the second year this will be extended to the GaAs quantum dot system. The long decoherence time of nuclear spin states also make quantum dots a promising candidate for qubits. In the final part of this project, an implementation of quantum protocols for quantum computing on quantum dot systems will be explored. It has already been demonstrated that a quantum dot-based qubit can be controlled to a high fidelity showing that this is a promising route to quantum computation. This project will build on this and research the implementation of Grover's search algorithm on a central spin system. It will also research the computational limitations of a quantum dot system and establish any limits to the kinds of algorithms that can be implemented.