MUCONTROL - Controlling muon states

凝聚态物理学的一个中心目标是理解处于长程有序边缘的系统。例如，术语自旋液体描述了物质的强相互作用磁性状态，其中强相互作用不会导致低温长程有序状态（如铁磁性或反铁磁性），而是导致非磁性的“量子无序”基态。有趣的是，尽管没有显示出长程磁序，但这样的系统通常可以显示出拓扑有序，这是由非常高的纠缠度造成的，其中基态由自旋对或自旋集合的量子叠加组成。为了理解这样的系统，重要的是要有一个高灵敏度的局部磁探针，理想的是一个操作与单自旋检测。自旋极化的μ子提供了这样一种灵敏的局部磁探针，该项目的中心是推进μ子技术，用于研究自旋液体等微妙的磁性系统。新项目的一部分将导致一些新的方法来理解和提取材料中的μ子位置，包括自旋液体。该项目的第二部分将把μ子方法与现有的脉冲核磁共振和电子自旋共振技术结合起来。而不是坐下来观察样品中的μ子进动（就像我们目前所做的那样），我们将能够使用高度指定的射频和微波脉冲序列来直接控制样品中的自旋。这将允许尝试全新的实验，该项目有可能从根本上改变我们使用μ子研究自旋液体物理的方式。

A central goal of condensed matter physics is to understand systems which are on the verge of long-range order. For example, the term spin liquid describes a strongly-interacting magnetic state of matter in which the strong interactions do not lead to a low-temperature long-range ordered state (such as ferromagnetism or antiferromagnetism) but instead result in a non-magnetic 'quantum disordered' ground state. Intriguingly, despite showing no long-range magnetic order, such systems can often show topological order resulting from an anomalously high degree of entanglement in which the ground state consists of a quantum superposition of pairs or collections of spins. To understand such systems, it is important to have a highly-sensitive local magnetic probe, ideally one operating with single spin detection. Spin-polarized muons provide just such a sensitive local magnetic probe, and this project is centred around advancing the muon technique for studying delicate magnetic systems such as spin liquids. One strand of the new project will lead to some new methods for understanding and extracting muon sites in materials, including spin liquids. A second strand of the project will marry muon methods with established pulsed nuclear magnetic resonance and electron spin resonance techniques. Rather than sitting back and watching the muons precess in the sample (as we do at present), we will then be able to use highly-specified sequences of radio frequency and microwave pulses to directly control the spins in the sample. This will allow entirely new experiments to be attempted and this project has the potential to radically alter the way we use muons to study spin liquid physics.