Integrated Quantum Frequency Combs for Cluster States Generation

量子计算，曾经是一个纯粹的理论梦想，正在成为现实。在过去的两年里，即2019年和2020年，量子计算机的优势首次得到了展示，也就是说，量子计算机可以在合理的时间内执行任何经典超级计算机都无法解决的任务。在这些相互竞争的技术中，光子学和超导电路是仅有的两种达到量子优势的技术。在这两种情况下，未来的挑战是可扩展性：目前的量子机器只能处理有限数量的量子比特，限制了它们在解决概念验证问题上的应用。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，是有用的，必须生活在一个成熟的技术，支持可扩展性与增加的复杂性和商业可行性制造的集成组件。集成光子满足这两个要求。它可以依靠在过去四十年中开发的用于电信和数据处理的大量工具和设备，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上述簇态的产生-集成光子学的一个最近的和引人注目的成功是实现了片上频率梳（微梳）。频率梳，由许多等距离频率（浅色）组成的电磁场，是计量学和光谱学的强大资源。通过集成光子学将它们从笨重的大块系统转变为几平方毫米的芯片，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，并自然地着陆以托管可扩展量子计算所需的簇态。为了将一个完整的频率梳转换成一个团簇态，它的所有频率模必须是纠缠的，也就是说，共享同一个量子态。在这里，我提出了一个解决这个问题的研究计划：基于频率梳产生一个集成的集群状态。在这个建议中开发的研究将揭示集成量子频率梳的量子计算的潜力。这将促进英国政府和研究委员会确定的一些战略应用，例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.