Quantum computing and communication with spin-photon interfaces

该项目属于ESPRC量子技术研究领域。该项目的重点是量子通信技术，以及如何利用网络中的节点执行量子信息处理任务。特别是，这项工作将探索GaAs量子点以及更广泛地说用于量子存储和量子计算的中心自旋系统的潜力。相干光物质接口是量子存储器的主要候选者，因为它们可以在量子状态下存储量子比特，具有较长的相干时间，并能够进行单光子控制。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。该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，来探索GaAs量子点以及更一般的中心自旋系统用于量子信息的潜力。该项目最初将专注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能够实现量子态的远距离传输。量子中继器协议包括在附近的纠缠光子上同时进行钟态测量，以在更长的距离上传输状态。距离越长，确保这些测量同时进行就变得越困难，因此需要量子存储器来在必要的时间内保持状态，以便进行每一次测量。在第一年，这个方案将适用于中心自旋系统和量子比特的相干性，并将决定量子比特存储和检索的保真度。在此基础上，还将对在GaAs量子点中产生光子簇态方案进行模拟。单光子系统的损失严重影响了系统的保真度，而团簇状态的产生意味着信息是共享的，并且系统对少数光子的损失是健壮的。已经研究了在钻石颜色中心创建一个簇，并将在第二年将这一研究扩展到砷化镓量子点系统。核自旋态的长消相干时间也使量子点成为量子比特的一个有前途的候选者。在本项目的最后部分，将探索用于量子计算的量子协议在量子点系统上的实现。已经证明，基于量子点的量子比特可以被控制到高保真，这表明这是一条很有前途的量子计算途径。本项目将以此为基础，研究格罗弗搜索算法在中央自旋系统上的实现。它还将研究量子点系统的计算限制，并对可以实现的算法种类建立任何限制。

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.