Understanding Quantum Non-Equilibrium Matter: Many-Body Localisation versus Glasses, Theory and Experiment

多体系统包括从简单的金属到复杂的有机分子，一直到活细胞的一切。虽然它们的物理学可能非常复杂，但这种复杂性通常是无关紧要的，因为大多数这样的系统在单独放置时会发生热分解，通过这个过程，关于它们的准备历史和初始状态的大多数信息都会丢失。想象一下把牛奶倒进咖啡或茶中：有许多不同的重要细节描述了这个过程--速度、牛奶量、牛奶壶的角度和位置、牛奶温度等等。所有这些参数都是预测当人们开始搅拌茶时所看到的复杂湍流模式所必需的。然而，在很长一段时间里，所有这些复杂性都被隐藏起来，我们只看到一种均匀的褐色液体。这种行为是遍历系统的典型特征，也是统计力学的核心;它允许我们对一个只给出少数参数（如总能量）的系统做出具体的预测。然而，物理学知道这种行为的例外。特别是，近年来，多体局域化（MBL）现象已经成为相互作用量子系统中没有热化和非遍历性的新范式。在这些系统中，所有的自由度都被外部无序所局限，因此彼此部分解耦并停止热化。特别是，可以证明这些系统对它们的初始条件保持了更好的局部记忆。例如，这种特殊的效应可能在未来被利用来设计更好的材料，以减少退相干的量子比特-即使一些信息泄漏到本地环境中，它也会在本地保持更长的时间。虽然MBL是一种新的量子效应，但在经典系统中，缓慢动力学和非遍历性的范例是玻璃化转变，其中流体系统-例如液体，胶体悬浮液或甚至颗粒混合物-在低温或高密度下停止流动并失去平衡。在这里，我们寻求支持诺丁汉和剑桥之间的一个新的理论实验合作，旨在发展的非平衡量子多体系统的核心方面的基本理解。特别是，我们建议建立MBL和玻璃之间的连接，从而揭示量子慢弛豫和非遍历性的新机制，具有潜在的影响，设计和控制的新型量子非平衡材料和设备。我们的团队由在实验和理论原子物理学，统计物理学和凝聚态方面具有丰富经验的研究人员组成，他们对MBL，玻璃，开放量子系统以及与该提案直接相关的其他主题做出了重要贡献。这个联合项目将使我们能够携手合作，使新的理论思想可以在实验中迅速得到测试，直接反馈到理论发展中。

Many-body systems comprise everything from simple metals, over complicated organic molecules, all the way to living cells. While their physics can be extremely complex, this complexity is however often mostly irrelevant, as most such systems will - when left alone - thermalise, a process through which most information about their preparation history and their initial state is lost. Think of pouring milk into your coffee or tea: there are many different important individual details describing this process - how fast, how much milk, angle and position of milk jug, milk temperature, and so on. All of those parameters are needed to predict the intricate turbulent pattern seen when one starts stirring the tea. At long time, however, all this complexity is hidden and we see merely a homogeneous brownish liquid. This behaviour is typical of ergodic systems and central to statistical mechanics; it allows us to make concrete predictions about a system given only a handful of parameters such as total energy. Physics knows, however, about exceptions to this behaviour. In particular, in recent years, the phenomenon of many-body localisation (MBL) has emerged as a new paradigm for the absence of thermalisation and non-ergodicity in interacting quantum systems. In these systems, all degrees of freedom become localised by an external disorder, and are therefore partially decoupled from each other and cease to thermalise. In particular, it could be shown that these systems keep a much better local memory of their initial conditions. This peculiar effect might for instance be exploited in the future to design better materials to host quantum bits with reduced decoherence - even if some information leaks into the local environment, it will remain local for much longer. While MBL is a novel quantum effect, in classical systems the paradigm of slow dynamics and non-ergodicity is the glass transition, whereby fluid systems - such as liquids, colloidal suspensions or even granular mixtures - cease to flow and fall out of equilibrium at low temperatures or high densities. Here, we seek support for a new theory-experiment collaboration between Nottingham and Cambridge aimed at developing a fundamental understanding of central aspects of non-equilibrium quantum many-body systems. In particular, we propose to establish the connections between MBL and glasses, thereby unveiling new mechanisms for quantum slow relaxation and non-ergodicity, with potential implications for the design and control of novel quantum non-equilibrium materials and devices. Our team comprises researchers with ample experience in experimental and theoretical atomic physics, statistical physics and condensed matter, who have made central contributions to MBL, glasses, open quantum systems, and other topics directly related to this proposal. This joint project will allow us to work hand-in-hand such that new theoretical ideas can quickly be tested in the experiment, which directly feeds back into theoretical developments.