QSUM: Quantum Science with Ultracold Molecules

世纪以来，科学家们一直对量子力学着迷，有时甚至感到困惑。量子力学是一种在微观层面上控制原子、分子乃至所有物质的理论。这个理论的核心是两个概念：（1）波粒二象性-粒子，如原子中的电子，可以表现得像波，光波可以表现得像粒子;（2）纠缠-一旦两个（或多个）粒子相互作用，无论它们相距多远，它们都不能被视为独立的实体。这些固有的量子现象是各种物理效应的核心，但它们的作用往往极难阐明。例如，在固体材料中，每个原子都与许多其他原子相互作用，预测和理解量子行为将如何表现出来是非常具有挑战性的，但它会导致高温超导性和特殊形式的磁性等效应。我们的计划将通过研究冷却到非常低的温度的分子的行为来促进对这些复杂量子系统的理解，我们可以隔离它们的量子行为。在这方面，分子的使用至关重要。它们丰富的内部结构意味着它们与电场和微波场强烈耦合，并且与原子相比，它们之间的相互作用距离更远。在推进我们对分子量子科学的理解过程中，我们还将学习如何利用它们的特性来构建新的设备，包括具有特殊灵敏度的传感器，能够解决以前无法解决的问题的计算机，以及可以设计新材料，磁体和超导体的模拟器。我们需要发展操控单个分子量子特性的能力。实现这一目标的第一步是消除通常隐藏其量子行为的热运动。我们已经开发出了使用固态和气相分子实现这一目标的方法。在固态，我们已经证明，某些有机染料分子，当嵌入在一个合适的固体冷却到低温温度，表现为接近理想的两能级量子系统。这种分子具有完美的特性，可以作为量子光和量子物质之间的界面-这是许多未来量子设备的重要组成部分。我们将学习如何利用这些特性按需生成单个光子，控制单个光子并存储量子信息。在气相中，我们扩展了激光冷却的方法，并开发了新技术，将分子冷却到绝对零度以上百万分之一度以内。在这个量子体系中，完全控制分子的内部状态和运动是可能的。通过这种控制，我们可以学习如何将分子耦合到微波和光波导上，如何将分子捕获在芯片上，如何组装有序的分子阵列来复制真实的材料的晶体结构，以及如何探索分子之间的相互作用如何控制多粒子系统的行为。这些雄心勃勃的目标需要激进的进步，我们将通过一系列与最先进的理论密切相关的相互关联的实验来实现。对于孤立分子，我们将发展对单个分子及其与单个光子耦合的控制;对于相互作用分子的小阵列，我们将控制简单几何中的相互作用和纠缠;对于二维和三维晶格，我们将理解强相互作用多粒子系统的复杂行为。通过这些项目，我们的方案将为基于分子量子控制的未来广泛的科学进步和技术应用奠定基础。

For over a century, scientists have been fascinated, and at times mystified, by quantum mechanics, the theory that governs atoms, molecules and, indeed, all matter at a microscopic level. Central to this theory are two concepts: (1) Wave-particle duality - the idea that particles, such as electrons in an atom, can behave like waves and that light waves can behave like particles, and (2) entanglement - the concept that once two (or more) particles have interacted, they cannot be treated as independent entities no matter how far apart they are. These inherently quantum phenomena are at the heart of a wide range of physical effects, but their role is often extremely difficult to elucidate. For example, in solid materials, where every atom interacts with many other atoms, it is very challenging to predict and understand how the quantum behaviour will manifest itself, and yet it leads to effects, such as high-temperature superconductivity and special forms of magnetism. Our Programme will advance the understanding of these complex quantum systems by studying the behaviour of molecules cooled to very low temperatures where we can isolate their quantum behaviour. In this respect, the use of molecules is crucial. Their rich internal structure means they couple strongly to electric and microwave fields, and interact with each other over a much greater distance compared with atoms. In advancing our understanding of the quantum science of molecules, we will also learn how to harness their properties to build new devices, including sensors of exceptional sensitivity, computers capable of solving previously unsolvable problems, and simulators that can design new materials, magnets and superconductors.To study the quantum science of molecules in a controlled and systematic way, we need to develop the ability to manipulate the quantum properties of individual molecules. The first step towards this goal is to remove the thermal motion that normally hides their quantum behaviour. We have already developed methods to achieve this both using molecules in the solid state and in the gas-phase. In the solid state, we have demonstrated that certain organic dye molecules, when embedded in a suitable solid cooled to cryogenic temperatures, behave as near-ideal two-level quantum systems. Such molecules have the perfect properties to act as interfaces between quantum light and quantum matter - an essential building block of many future quantum devices. We will learn how to exploit these properties to generate single photons on demand, control individual photons, and store quantum information. In the gas phase, we have extended the methods of laser cooling and developed new techniques to cool molecules to within a millionth of a degree above absolute zero. In this quantum regime, it is possible to exert complete control over the internal state and motion of the molecules. With this control we can learn how to couple molecules to microwave and optical waveguides, to trap molecules on chips, to assemble ordered arrays of molecules that replicate the crystalline structure of real materials, and to explore how the interactions between molecules govern the behaviour of the many-particle system. These ambitious goals calls for radical advances, which we will deliver through a set of interconnected experiments intimately linked to state-of-the-art theory. With isolated molecules we will develop the control of single molecules and their coupling to single photons; with small arrays of interacting molecules we will control interactions and entanglement in simple geometries; and with two- and three-dimensional lattices we will understand the complex behaviour of strongly interacting many-particle systems. Through these projects, our Programme will lay the foundations for a broad range of future scientific advances and technological applications based on the quantum control of molecules.