Building Large Quantum States out of Light

我们的目标是建立世界上最大的量子光子网络，在这个网络中，多达20个光子--光的基本粒子--连接在一起，产生一个巨大的、可控的量子系统。这一新工具将开辟物理学的重要领域，这些领域过于复杂，无法用常规方法进行研究，例如生物能量传输和高温超导。由于光子被用来传输信息，该网络还将形成一个平台，用于革命性的新量子技术，如超精密传感和全球有保证的安全通信。为了实现如此大的量子系统，我们将引入从根本上改变光子学可伸缩性的新技术。这将为未来更大的网络奠定基础，使英国成为新兴量子技术行业的领先者。一百多年来，我们已经知道原子和分子不按牛顿定律运动。相反，它们遵守量子力学定律。这些定律很奇怪，但它们解释了化学键是如何形成的，以及为什么硅芯片可以制造计算机。这些见解在20世纪推动了一场深刻的技术革命，跨越了医学、电信和计算机领域的非凡进步。现在很明显，我们目前对量子系统的了解只是冰山一角。虽然我们可以准确地理解两个粒子之间的量子效应，或者以近似的方式理解多个原子之间的量子效应，就像半导体晶体管的情况一样，但由许多粒子组成的大型物体无法详细分析。它们太复杂了，事实上，除了几个原子之外，它们甚至不能用超级计算机来模拟。问题是量子系统在某种意义上是模糊的，所以每个粒子都是一个分布，而不是一个单独的点。要描述许多粒子，需要分布的分布，等等。这种复杂性的爆炸式增长意味着，到目前为止，自然界中许多有趣的系统--生物学和医学、粒子物理学和材料科学--基本上都不能进行分析。详细研究复杂量子系统的唯一方法是建造一台机器，以一种量身定制的、可控的方式创建它们，这样我们就可以建立我们想要研究的真实系统的模型。在过去的二十年里，一门新的量子信息科学已经发展起来。除了将其应用于自然科学中的问题外，已有研究表明，大型可控量子系统可以支撑一系列变革性的新技术，包括可能出现比当今最好的计算机速度快得多的量子计算机。也许令人惊讶的是，量子计算的最先进方法之一涉及光子而不是原子。光子可以很容易地通过光纤传输，光纤是用于电信和互联网的一项成熟技术，而且它们几乎没有噪音。由于这些优点，短距离光学量子密码学已经可以商业使用。为了更进一步，实现量子信息科学最雄心勃勃的目标，并开启对复杂量子系统的研究，必须连接多个光子并对其进行精确操作。我们的目标是通过利用为现代电信行业开发的先进制造方法来构建一个约20个光子级别的大规模可控量子光子网络，以应对这一挑战。特别是，我们将使用二氧化硅集成光学器件--写入小玻璃芯片上的光电路--以最小的损耗连接光子。它们将连接到高效计数光子的超导探测器，以及可以存储光子并使网络同步的新型量子存储器。将量子存储器与这些高效技术相结合，将使网络能够以前所未有的规模运行，从而获得新物理和新技术。

We aim to build the world's biggest quantum photonic network, in which up to twenty photons, elementary particles of light, are connected to produce a large, controllable quantum system. This new tool will open up important realms of physics that have been too complex to study conventionally, such as biological energy transport and high-temperature superconductivity. Since photons are used to transport information, the network will also form a platform for revolutionary new quantum technologies like ultra-precise sensing and guaranteed-secure communication across the globe. To achieve such a large quantum system, we will introduce new techniques that fundamentally change the scalability of photonics. This will lay the ground for even larger networks in the future, establishing the UK as a leader in the nascent quantum technology industry.We have known for over a hundred years that atoms and molecules don't move according to Newton's laws. Instead, they obey the laws of quantum mechanics. These laws are strange but they explain how chemical bonds form and why silicon chips can make computers. These insights drove a profound technological revolution in the 20th century, spanning extraordinary advances in medicine, telecoms, and computing. It is now clear that our current knowledge of quantum systems is just the tip of the iceberg. While we can understand quantum effects between just two particles exactly, or between many atoms in an approximate way, as is the case for a semiconductor transistor, large objects composed of many particles cannot be analysed in detail. They are too complicated, and in fact beyond a few atoms, they cannot even be simulated with a supercomputer. The problem is that quantum systems are fuzzy, in a sense, so each particle is a distribution, not a single point. To describe many particles requires distributions of distributions of distributions and so on. This explosion in complexity means that many interesting systems in nature - in biology and medicine, particle physics and materials science - have so far been largely closed to analysis. The only way to study complex quantum systems in detail is to build a machine that can create them in a tailored, controllable way, so that we can build models of the real systems we want to study.Over the past two decades, a new science of quantum information has developed. In addition to their application to problems in the natural sciences, it has been shown that large controllable quantum systems can underpin a host of transformative new technologies, including the possibility of quantum computers that are exponentially faster than today's best computers. Perhaps surprisingly, one of the most advanced approaches to quantum computation involves photons instead of atoms. Photons can easily be transported by optical fibres, which are a mature technology used for telecoms and the internet, and they experience almost no noise. Because of these advantages, optical quantum cryptography over short distances is already commercially available.To go further and realise the most ambitious goals of quantum information science, and to open up the investigation of complex quantum systems, many photons must be connected and precisely manipulated. We aim to meet this challenge by leveraging advanced fabrication methods developed for the modern telecoms industry to build a large-scale controllable quantum photonic network, at the level of around twenty photons. In particular, we will use silica integrated optics -- circuits for light written on small glass chips -- to connect photons with minimal losses. These will be joined to superconducting detectors that count photons with high efficiency, and novel quantum memories that can store photons and synchronise the network. Combining quantum memories with these highly efficient technologies will enable the network to operate with at an unprecedented scale, giving access to new physics and new technologies.