Quantum interface engineering with solid-state spins and photons

该项目属于EPSRC“量子技术”研究领域。该项目专注于实验量子通信技术，特别是使用III-V量子点(QD)，它们被广泛认为是用于量子光网络的领先量子节点候选之一。它将研究新一代晶格匹配的GaAs量子点，这有望在自组装InGaAs量子点的自旋量子比特(Qbit)的相干性质方面取得相对于最先进水平的重大改进。总体目标是证明它们可以作为量子网络节点，这需要同时展示：高效的光子收集、量子比特控制和核量子存储器。这将允许量子点与其固态自旋量子位纠缠足够长的时间来产生光子，以用于与其他量子节点联网以实现量子网络。最初的重点将是改善量子点中自旋量子位与出射光子之间的光学界面。提高光子收集效率是至关重要的，因为尽管GaAs量子点在其长自旋相干时间方面显示出巨大的前景，这是保持量子态的重要指标，但它们在光子收集效率方面落后于其他候选量子点(如InGaAs)。我们的愿景是将量子发射器(QD)放置到光子微腔中，这将增强发射和耦合成光纤模式，以便进行长距离传输。接下来，我们将演示量子比特对QD电子自旋的控制，这将是全光学执行的。这种在高效光学界面内进行自旋控制的组合将是独一无二的，并将允许进行概念验证演示，例如确定性光子-光子量子门。最后，利用单电子和近端核自旋之间的超精细相互作用，利用电子的光学可寻址存储，使量子存储成为可能，使这个基于量子点的量子节点拥有专用的量子存储。该项目旨在为构成量子通信和计算网络主干的多种量子协议提供基准结果，例如光子量子比特之间的量子门、量子中继态的生成以及纠缠的分配和存储。实现可行的量子光网络将使量子节点之间实现真正的量子互联网，为完全私人通信(由量子力学原理确保)、量子密码学和分布式量子计算铺平道路。这项工作是与剑桥大学的量子光学材料和系统小组、林茨约翰尼斯开普勒大学的半导体物理小组和牛津大学的光子纳米材料小组合作完成的。

This project falls within the EPSRC "quantum technologies" research area. The project focuses on experimental quantum communication technologies, using in particular III-V quantum dots (QDs), which are widely considered to be amongst the leading quantum node candidates for use in quantum optical networks. It will investigate a new generation of lattice-matched GaAs QDs, which promise a major improvement in the coherence properties of spin quantum bits (qubits) relative to the state of the art in self-assembled InGaAs QDs. The overall objective is to demonstrate that they can serve as a quantum networking node, which requires showing simultaneously: high-efficiency photon collection, qubit control, and a nuclear quantum memory. This will allow the generation of photons from the QD which are entangled with its solid-state spin qubits for a sufficient time that they can be used to network with other quantum nodes to realize a quantum network.Initially the focus will be on improving the optical interface between the spin qubits in the QDs and the outgoing photons. Enhancing photon collection efficiency is crucial, as while GaAs QDs have shown great promise in terms of their long spin coherence times, an important metric for preserving the quantum state, they lag other QD candidates (e.g. InGaAs) in terms of photon collection efficiency. The vision is to place the quantum emitter (QD) into a photonic microcavity, which would enhance emission and coupling into a fibre mode for long distance transmission. Next, we will demonstrate qubit control of the QD electron spin, which will be performed all-optically. This combination of spin control within an efficient optical interface will be unique, and will allow proof-of-concept demonstrations such as a deterministic photon-photon quantum gate. Finally, a quantum memory will be made possible by capitalizing on the hyperfine interaction between the single electron and the proximal nuclear spins to facilitate an optically addressable memory using the electron, enabling this QD-based quantum node to have dedicated quantum memories. The project aims to deliver benchmarking results on a multitude of quantum protocols forming the backbone of a quantum communication and computing network, such as quantum gates between photon qubits, generation of quantum repeater states, and distribution and storage of entanglement. Realizing a viable quantum optical network would enable a truly quantum internet between quantum nodes, paving the way for fully private communications (ensured by the principles of quantum mechanics), quantum cryptography, and distributed quantum computing. The work is performed in collaboration with the Quantum Optical Materials and Systems group at the University of Cambridge, the Semiconductor Physics group at Johannes Kepler University Linz, and the Photonic Nanomaterials Group at the University of Oxford.