New Physics at the Interface Between the Classical and Quantum Worlds

凝聚态物理学是一个具有技术和基础科学重要性的领域。现代技术越来越依赖于物质在最小尺度上的量子行为。制造量子计算机的竞赛试图非常直接地利用这种行为，但量子力学在更熟悉的技术中很重要：晶体管、超导体和硬盘驱动器中的读头都关键地依赖于固体中电子的量子力学。理解固体中电子的集体量子行为不仅是技术的重要驱动力，而且还提出了对其他科学领域有影响的基本问题。举一个典型的例子，超导体在磁场中悬浮（迈斯纳效应）的解释是由安德森-希格斯机制提供的-新的理论思想在指导实验向富有成效的方向发展方面具有重要意义，而实验中令人困惑的结果在帮助理论发展方面也是必不可少的-解开这些谜题可以引出对更广泛领域产生影响的基本原理。我发展数学理论来预测实验中尚未发现的新效应，并与实验学家合作，了解如何观察到这些新效应。我们一起确定哪些实验异常可能在当前理论中被理解。那些不能为理论研究提供重要指导和新方向的。我的大部分时间都花在研究量子临界系统上。这些系统在量子世界和经典世界之间保持平衡-它们遵守的规则部分类似于日常经验的经典规则，部分类似于最小尺度的奇异量子规则。许多材料的电子行为都是量子临界的，它们有一个物理学家称之为普适性的特性：它们在低能和长距离下的行为基本上与高能和短距离下的行为无关。正因为如此，他们提供了一个论坛，在那里我们可以理解经典世界如何从微观尺度上的量子行为中出现的一般特征，而不会被材料之间的差异等细节所分散。

Condensed matter physics is an area of both technological and fundamental scientific importance. Modern technology isincreasingly dependent upon the quantum behaviour of matter on the smallest scale. The race to make a quantumcomputer seeks to use this behaviour very directly, but quantum mechanics is important in more familiar technology:transistors, superconductors and the read heads in hard drives all depend crucially upon the quantum mechanics ofelectrons in solids.Understanding the collective quantum behaviour of electrons in solids is not only an important driver of technology, but italso raises fundamental issues with impact in other areas of science. To take a topical example, the explanation of whysuperconductors hover in magnetic fields (the Meissner effect) was provided by the Anderson-Higgs mechanism --- thevery same mechanism that is now thought to provide the origin of mass itself and which is currently being investigated atFERMILAB the LHC in CERN.There is a tremendous symbiosis between theory and experiment in condensed matter physics. New theoretical ideas arecrucial in guiding experiment in fruitful directions and puzzling results from experiment are essential in aiding thedevelopment of theory --- unraveling these puzzles can lead to fundamental principles that have an impact much furtherafield.I study the theory of the collective quantum behaviour of electrons. I develop mathematical theories predicting neweffects not yet seen in experiment and work with experimentalists to understand how these new effects can be observed.Together, we determine which experimental anomalies might be understood within current theories. Those that cannotprovide important guidance and new directions for theoretical investigation.Much of my time is spent studying quantum critical systems. These systems are balanced between the quantum andclassical worlds --- they obey rules that are partly like the classical rules of everyday experience and partly the strangequantum rules of the very smallest scale. A large variety of materials have electronic behaviour that is quantum critical.They have a property that physicists call universality: their behaviour at low energy and long distances is largelyindependent of the high energy and short distance behaviour. Because of this, they provide a forum in which we canunderstand general features of how classical world emerges from the quantum behaviour on the microscopic scalewithout being distracted by details such as differences between materials.