Quantum computing and communication with spin-photon interfaces

该项目属于ESPRC量子技术研究领域。该项目侧重于量子通信技术，以及如何利用网络中的节点来执行量子信息处理任务。特别是，这项工作将探索砷化镓量子点和更普遍的中央自旋系统在量子存储和量子计算方面的潜力。相干光物质界面是量子存储器的主要候选者，因为它们可以将量子比特存储在其量子态，具有较长的相干时间并能够实现单光子控制。量子点中电子自旋和核自旋系综之间的超精细相互作用使它们成为极好的宿主。本项目旨在通过扩展系统和控制协议的理论模型，并在实际参数下对结果进行数值模拟，探索砷化镓量子点和更广泛的中心自旋系统在量子信息方面的潜力。最初，该项目将侧重于量子中继器协议的建模和分析。基于量子存储器的量子中继器实现了量子态的远距离传输。量子中继器协议包括对附近纠缠的光子同时进行钟态测量，以便在更远的距离上传输状态。距离越长，确保这些测量同时进行就越困难，因此需要量子存储器在必要的时间内保持状态以进行每次测量。在第一年，该方案将适用于中心自旋系统和量子比特相干性，并确定量子比特存储和检索的保真度。除此之外，还将对GaAs量子点中光子团簇状态方案的创建进行模拟。单光子系统的损耗极大地影响了系统的保真度，而簇态的产生意味着信息是共享的，并且系统对少量光子的损耗具有鲁棒性。在钻石色中心建立一个簇已经被研究过了，在第二年，这将扩展到砷化镓量子点系统。核自旋态的长退相干时间也使量子点成为量子比特的一个有希望的候选者。在本课题的最后一部分，将探讨量子点系统上量子计算的量子协议的实现。已经证明，基于量子点的量子比特可以被控制到高保真度，这表明这是量子计算的一条有前途的途径。本项目将以此为基础，研究Grover搜索算法在中心自旋系统上的实现。它还将研究量子点系统的计算限制，并确定可以实现的各种算法的限制。

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.