Quantum Matter in and out of Equilibrium

物质——我们周围世界里的物质——在它的许多部分协同作用时被“浓缩”了。凝聚态物质的例子实际上是无限的，因为任何物质都是由许多单个原子组成的。在微观尺度上对凝聚态物质的研究不可避免地涉及到量子物理学——适用于小物体（如单个原子或电子）的自然定律。利用量子理论研究凝聚态物质是我们研究的核心。量子凝聚态理论包含了现代科学中一些最重要、最困难和最有趣的问题。原因是，当一个大系统的许多组成部分集体行动时，量子力学的影响会变得更加复杂和令人惊讶。意想不到的现象可以在大尺度上“出现”，而与微观性质没有任何相似之处。例如，许多电子可以集体“超导”，在绝对没有能量损失的情况下，在很远的距离上携带电流。在某些系统中，更壮观的突现行为是电子“分馏”，即电子有效地分裂成碎片！量子凝聚态理论是基本的学术兴趣，因为发生的奇怪和令人惊讶的事情。它对于发展一系列广泛的技术也是必不可少的；毫不夸张地说，计算机和通信工业是建立在上个世纪对量子凝聚态理论的发现和理解的基础上的。虽然我们的工作主要是学术性的，但我们目前的探索很可能为未来几年的新行业铺平道路。牛津量子凝聚态理论小组使用现代工具和技术来解开量子凝聚态的谜题，推动知识的边界，并为未来的技术奠定基础。研究的主要目标是寻找复杂量子系统的结构和模式，具体项目是由特定动机和方法联合起来的连贯方向。这项工作概括为四个主题，都处于现代研究的前沿：(1)拓扑物质的表征和检测，这是一种特别有前途的未来量子技术的物质类型，最近才发现，到目前为止，它在理论上和实验上都没有得到彻底的理解。它的一个特点是分馏化。(2)物质的非平衡量子态（Non-equilibrium Quantum States of Matter），这是上个世纪发展起来的，传统的热力学和统计力学工具无法很好地描述的量子系统。(3)拓扑相的几何描述——从主题(1)中理解拓扑物质的最佳方法通常使用几何语言。(4)相关量子物质的无序性——某些类型的物质只出现在有许多杂质或原子排列不规则的系统中。我们从这些探索中获得的理解将反过来开辟新的科学方向。

Matter -- substance in the world around us -- is "condensed" when its many pieces act in concert. Examples of condensed matter are virtually limitless, since any material is comprised of many individual atoms. The study of condensed matter on a microscopic scale inevitably involves quantum physics -- the laws of nature that apply to small objects such as individual atoms or electrons. Using quantum theory to study condensed matter lies at the heart of our research. Quantum condensed matter theory contains some of the most important, most difficult, and most intriguing questions in modern science. The reason is that the effects of quantum mechanics are all the more complex and surprising when many constituent parts of a large system behave collectively. Unexpected phenomena can "emerge" on large scales that bear no similarity to the microscopic properties. For example, many electrons can collectively "superconduct", carrying electrical current over huge distances with absolutely no loss of energy. An even more spectacular emergent behaviour in some systems is electron "fractionalisation", where the electron effectively has split into pieces!Quantum condensed matter theory is of fundamental academic interest because of the strange and surprising things that occur. It is also essential for the development of a vast range of technologies; it is no exaggeration to say that the computer and communications industries are built upon a foundation of discoveries and understanding in the quantum condensed matter theory of the last century. While our work is mainly academic in nature, our current explorations may very well pave the way for new industries in the years to come. The Oxford quantum condensed matter theory group use modern tools and techniques to unravel the puzzles of quantum condensed matter, to push forward the boundaries of knowledge, and to lay the groundwork for technologies of the future. The research is motivated by the overarching goal of finding structure and patterns in complex quantum systems, and the particular projects are coherent directions united by both specific motivations and methods. The work is summarized by four themes, all at the forefront of modern research:(1) Characterisation and Detection of Topological Matter, a particularly promising type of matter for future quantum technologies, only discovered recently, which so far has defied thorough understanding both theoretically and experimentally. One of its specific features is fractionalization.(2) Non-equilibrium Quantum States of Matter, quantum systems which are not well described by the conventional tools of thermodynamics and statistical mechanics developed in the last century. (3) Geometric Descriptions of Topological Phases -- the best approach to understanding topological matter from Theme (1) often uses a geometrical language. (4) Disorder in Correlated Quantum Matter -- some types of matter appear only in systems with many impurities or irregularities in the arrangements of atoms.The understanding we gain from these explorations will in turn open up new scientific directions.