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

工程纳米级系统提供了接触物质量子特性的途径，预示着物理学和技术领域的一场革命。控制单个量子物体，如单个电子或光子，以及它们之间的相互作用，提供了设计相关性的手段，使量子技术比目前的同类技术取得革命性的进步。静止物质和飞行的光学量子比特（qubit）之间的接口是相互连接的基本组成部分，这将使量子技术在大规模上有用。固态器件显示出强耦合的光-物质界面、高效的光收集和相干物质节点的量子控制。增强自旋和光学相干特性的制造技术的进步，以及对复杂环境建模的重要理论努力，已经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外，这种光活性固态平台由于易于与经典光学和电气元件组合集成，为开发提供了独特的长期优势。该项目将整合下一代固态量子网络节点，结合量子光学研究界的最新发展——光学器件集成、全光电子自旋控制和核自旋相干性和控制——提供一个在光学相干性和效率、量子比特控制和量子存储器寿命等综合指标上优于其他候选技术的平台。该提案包括通过利用最近在系统中已经被称为最佳单光子源的两个突破来实现这种组合- III-V半导体量子点：(1)开放光学微腔作为多功能接口，达到强光-物质耦合和高收集效率；(2)无应变GaAs量子点作为相干物质量子比特的宿主，初步测量表明，在其上相干时间比目前的状态（InAs量子点）提高了两个数量级。作为本提案的第一个主要基准和主要成果，确定性量子门将在两个光子量子比特之间执行，利用新一代量子点的光学和自旋相干性。该提案的目标是在两个光子量子比特之间达到超过1MHz的纠缠率，同时实现几个百分点的错误率-比先前在光学领域的尝试提高了四个多数量级的速率保真度产品。这将作为一个概念验证，将该平台建立为大规模量子光学器件阵列投资的最佳选择。最后，开发这种砷化镓量子点平台有望为领先的商业单光子发射器配备长寿命的核自旋存储器，这是这种精致的光子平台所缺失的部分。这将使远距离量子节点间的长期纠缠成为可能，这是通往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.