Deterministic quantum gate between photons in a next-generation light-matter interface

能够获得物质量子性质的工程纳米系统预示着物理和技术的一场革命。对单个量子物体，如单个电子或光子，以及它们之间相互作用的控制，提供了设计关联的手段，使量子技术比目前的同类技术有了革命性的进步。静止物质和飞行的光学量子比特(量子比特)之间的界面是互连的基本构件，这将使量子技术在大规模应用。固态器件已经显示出强耦合的光-物质界面，高效的光收集，以及相干物质节点的量子控制。在增强自旋和光学相干性质的制备技术方面的进展，加上在模拟复杂环境方面的重要理论努力，在这些领域取得了重大进展。事实上，最近在半导体中使用光学可寻址自旋的演示包括对贝尔不等式的无漏洞测试，基于测量的量子计算中涉及的光子态的生成，以及量子互联网原语的实现。除了超冷原子和超导电路，这种光学活性固态平台由于易于与经典光学和电子元件相结合而提供了独特的长期优势。该项目将构建下一代固态量子网络节点，该节点结合了量子光学研究领域的最新发展--光学设备集成、全光电子自旋控制以及核自旋相干和控制--以提供一个在光学相干和效率、量子比特控制和量子存储器寿命等综合指标上超越其他候选技术的平台。这项建议包括通过利用已被称为最佳单光子源的系统-III-V半导体量子点的两项最新突破来实现这一组合：(1)开放光学微腔作为实现强光物质耦合和高收集效率的通用接口，以及(2)无应变GaAs量子点，作为相干物质量子比特的宿主，并且初步测量表明，其相干时间比最先进的(InAs量子点)提高了两个数量级。作为这一提议的第一个主要基准和主要成果，将在两个光子量子比特之间执行确定性量子门，利用这种新一代量子点的光学和自旋相干性。这一提议旨在达到两个光子量子比特之间超过1 MHz的纠缠速率，同时实现几个百分点的错误率-与以前在光域的尝试相比，错误率保真度积提高了四个数量级以上。这将作为一个概念验证，将该平台确立为投资大规模量子光学设备阵列的最佳选择。最后，开发这个GaAs量子点平台有望为领先的商业单光子发射器配备长寿命核自旋存储器，这是这个否则精致的光子学平台所缺少的部分。这一增加将允许展示跨越遥远的量子节点的长期纠缠，这是迈向量子互联网的关键一步，在量子互联网中，这种纠缠可以用作通信和计算的资源。

Engineered nanoscale systems that provide access to the quantum properties of matter are heralding a revolution in physics and technology. Control over single quantum objects, such as a single electron or photon, and over interactions between them provides the means to engineer the correlations that make quantum technologies a revolutionary advance over their current counterparts. An interface between a stationary matter and a flying optical quantum bit (qubit) is a fundamental building block of the inter-connects that will make quantum technologies useful on a large scale. Solid-state devices have shown strongly coupled light-matter interfaces, efficient light collection, and quantum control of coherent matter nodes. Progress on fabrication techniques to enhance spin and optical coherence properties, combined with important theoretical efforts on modelling complex environments, have yielded significant gains in these areas. Indeed, recent demonstrations using optically addressable spins in semiconductors include a loophole-free test of Bell's inequalities, the generation of photonic states involved in measurement-based quantum computation, and the realisation of quantum internet primitives. Alongside ultracold atoms and superconducting circuits, such optically active solid-state platforms provide developments with distinct long-term advantages due to their ease of integration with combined classical optical and electrical elements. This project will put together a next-generation solid-state quantum networking node that combines the latest developments in the quantum optical research community -- optical device integration, all-optical electron spin control, and nuclear spin coherence and control -- to deliver a platform that outperforms other candidate technologies on the combined metrics of optical coherence and efficiency, quantum bit control, and quantum memory lifetime. This proposal consists of realising this combination by leveraging two recent breakthroughs in a system already known as the best single photon source - III-V semiconductor quantum dots: (1) open optical microcavities as a versatile interface to reach a strong light-matter coupling and high collection efficiency, and (2) strain-free GaAs quantum dots, as host for a coherent matter quantum bit, and on which preliminary measurements indicate a two orders of magnitude improvement in coherence time over the state of the art (InAs quantum dots). As a first major benchmark and the major deliverable of this proposal, a deterministic quantum gate will be performed between two photon qubits, leveraging the optical and spin coherence of this new generation of quantum dots. This proposal aims to reach beyond 1MHz entanglement rate between two photon qubits while achieving a few-percent error rate - a more than four orders of magnitude improvement of the rate-fidelity product over previous attempts in the optical domain. This will serve as a proof-of-concept to establish this platform as the optimal choice for investment towards large-scale arrays of quantum optical devices.Finally, developing this GaAs quantum dot platform promises to equip the leading commercial single-photon emitters with a long-lived nuclear-spin memory, the missing piece for this otherwise exquisite photonics platform. This addition would allow the demonstration of long-lived entanglement across distant quantum nodes, a crucial step en route to a quantum internet where such entanglement can be used as a resource for communication and computation.