Integrated Quantum Frequency Combs for Cluster States Generation

量子计算曾经是一个纯粹的理论梦想，现在正在成为现实。在过去的两年-2019年和2020年-见证了量子优势的首次展示，即量子计算机执行任何经典超级计算机在合理时间内无法解决的任务。在相互竞争的技术中，光子学和超导电路是唯一两项达到量子优势的技术。在这两种情况下，未来的挑战都是可扩展性：目前的量子机器只能处理有限数量的量子比特，将它们的应用限制在解决概念验证问题。该项目旨在开发一种高度复杂的量子态，称为簇态，它支持可扩展的光子量子计算方法。这样的状态要有用，必须依赖于由成熟技术制造的微型化组件，这种技术支持可伸缩性，增加了复杂性和商业可行性。集成光子学满足了这两个要求。它可以依赖于在过去40年中开发的大量用于电信和数据处理的工具和设备，并采用连接经典计算机的最新技术。该项目将使用集成光子学的最新发现和技术来实现在芯片上产生上述簇态。集成光子学最近和令人震惊的成功之一是在芯片上实现频率梳(微梳)。频率梳是由许多等距频率(浅色)组成的电磁场，是计量和光谱学的强大资源。通过集成光子学实现的小型化，将它们从笨重的大宗系统转变为几毫米平方的芯片，使集成频率梳成为最有前途的光子技术之一。频率梳具有数千到数百万个模式，并自然着陆以容纳可扩展量子计算所需的团簇状态。为了将一个集成频率梳转换为团簇状态，它的所有频率模必须是纠缠的，即共享相同的量子态。在这里，我提出了一个解决这个问题的研究方案：基于频率梳生成一个集成的团簇状态。在这个方案中开展的研究将揭示集成量子频率梳用于量子计算的潜力。这将促进英国政府和研究委员会确定的一些具有战略意义的应用，如时钟同步和量子技术的部署。

Quantum computing, once a purely theoretical dream, is becoming a reality. The last two years - 2019 and 2020 - have seen the first demonstrations of quantum advantage, that is, quantum computers performing tasks that cannot be solved by any classical supercomputer in a reasonable time. Among the competing technologies, photonics and superconducting circuits are the only two that reached quantum advantage. In both cases, the challenge ahead is scalability: the current quantum machines can only process a limited number of quantum bits, limiting their application to the solution of proof-of-concept problems.This project aims to develop a highly complex quantum state, called cluster state, that underpins a scalable approach to photonic quantum computing. Such a state, to be useful, must live on miniaturised components fabricated by a mature technology that supports scalability with increased complexity and commercial viability. Integrated photonics satisfies both these requirements. It can count on a large selection of tools and devices developed during the last forty years for telecommunications and data processing and employs the latest technologies that connect classical computers.This project will use the latest discoveries and technologies of integrated photonics for realising the generation of the aforementioned cluster states on-chip.One of the more recent and striking successes of integrated photonics is the realisation of frequency combs on-chip (microcombs). Frequency combs, electromagnetic fields composed by many equidistant frequencies (light colours), are a powerful resource for metrology and spectroscopy. Their miniaturisation via integrated photonics transformed them from cumbersome bulk systems to few millimetres squared chips, making integrated frequency combs one of the most promising photonic technologies.Frequency combs feature thousands to millions of modes and land themselves naturally to host the cluster states required for scalable quantum computation. To transform an integrated frequency comb into a cluster state all its frequency modes must be entangled, that is, sharing the same quantum state. Here, I propose a research programme that tackles this very problem: generating an integrated cluster state based on frequency combs.The research developed in this proposal will disclose the potential of integrated quantum frequency combs for quantum computing. This will boost a number of applications identified as strategic by the UK Government and Research Councils such as clock synchronisation and the deployment of quantum technologies.