Quantum simulation using interacting spins in solids

纳米尺度的非侵入性磁成像是理解原子尺度上有机和无机材料相互作用的关键。利用磁共振技术感知电子和核自旋已经改变了结构生物学和块状固态材料的研究。本文提出了一种基于金刚石单原子缺陷与金刚石表面电子自旋耦合的新型成像工具的开发和利用途径和方法。金刚石中的氮空位中心（NVs）是一种原子杂质，可以作为磁场、电场和温度的高度局部传感器。NV电子自旋可以通过光学显微镜来探测，而不需要与传感装置直接电接触。从杂质中收集的光包含有关其微观量子态的信息，这些信息将因其环境的任何变化而改变。例如，该系统允许将单个电子自旋定位到单个晶格位置，并且在一秒钟的积分时间内仅检测几百个核自旋。由于它是非侵入性的，并在环境条件下提供纳米尺度的空间分辨率，该传感器填补了成像技术的重要空白，在纳米尺度上提供了软、固态系统中探针结构和动力学的分辨率和灵敏度。然而，它的空间分辨率受到NV中心靠近金刚石表面的不稳定性的限制：如果它靠近金刚石表面超过几纳米，它的电荷状态就会改变，并且它不再能够充当量子传感器。这阻碍了它在亚纳米分辨率下研究感兴趣的样品中的核自旋，在那里会发生许多有趣的现象。本项目旨在开发一套新的基于金刚石表面电子自旋团簇的磁成像工具，以揭示迄今为止隐藏的亚纳米尺度的物理现象。我们将利用金刚石中单个NV中心与一小簇顺磁性金刚石表面自旋之间的偶极耦合来提供感兴趣的附近核自旋的埃级接近。我们将研究存在于小分子体积液体中的核自旋，用于亚纳米尺度的传感，我们将探测二维材料原子完美阵列中的核自旋。这种阵列为探索远程相互作用的二维多体系统中的纳米级自旋热化和局部化行为提供了一个平台。这为最终解决有关二维热化和多体定位的问题提供了一个令人兴奋的机会。据预测，这种由相互作用的自旋组成的系统将表现出长寿命的量子态，这与脆弱的量子系统暴露于与环境相互作用时通常观察到的快速热化相反。由于这种系统的复杂性，它们的行为不能通过传统的模拟来捕捉，并且需要使用所谓的量子模拟器：模拟器本身就是量子系统，并捕获感兴趣的物理相互作用和动力学。在这里，我们将处于一个独特的位置，通过自旋控制和哈密顿工程技术来探索这个多体量子模拟器的相空间。利用金刚石表面自旋，我们旨在揭示复杂自旋系统中的自旋热化动力学和多体效应。

Non-invasive magnetic imaging at the nanometre scale holds the key to understanding the interactions of organic and inorganic materials on the atomic scale. Sensing of electronic and nuclear spins using magnetic resonance techniques has already transformed structural biology and the study of bulk solid-state materials. This proposal sets out the path and methods to develop and exploit a new type of imaging tool based on single atomic defects in diamond coupled to electronic spins located right at the surface of diamond. Nitrogen vacancy centres (NVs) in diamond are atomic impurities that can serve as highly localised sensors for magnetic and electric fields, and temperature. The NV electronic spin can be probed through an optical microscope, not requiring direct electrical contacting of the sensing device. The light collected from the impurity contains information about its microscopic quantum state, which will be altered by any change in its environment. This system allows, for instance, the localization of individual electronic spins to single lattice sites and the detection of only a few hundred nuclear spins in one second of integration time. Because it is non-invasive and provides nanometre scale spatial resolution under ambient conditions, this sensor fills an important gap in imaging techniques, providing the resolution and sensitivity to probe structure and dynamics in soft and solid state systems on the nanometre scale. However, its spatial resolution is limited by the instability of the NV centre close to the surface of diamond: if it lies closer than a few nanometres to the diamond surface, its charge state changes and it is no longer able to act as a quantum sensor. This prevents its use for studying nuclear spins in samples of interest with sub-nanometre resolution, where many interesting phenomena occur. This project aims to develop a new set of magnetic imaging tools based on electronic spin clusters at the surface of diamond with the goal of revealing hitherto concealed physical phenomena at the sub-nanometre scale. We will exploit the dipolar coupling between a single NV centre in diamond and a small cluster of paramagnetic diamond surface spins to provide angstrom-scale proximity to nearby nuclear spins of interest. We will investigate nuclear spins residing in few-molecule volumes of liquids for sub-nm scale sensing and we will probe nuclear spins in the atomically perfect arrays of 2D materials. Such arrays provide a platform for exploring the nanoscale spin thermalisation and localisation behaviour in long-range interacting, two-dimensional, many-body systems. This presents an exciting opportunity to finally resolve questions regarding thermalisation and many-body localisation in two dimensions. It has been predicted that such systems composed of interacting spins will exhibit long-lived quantum states, contrary to the rapid thermalisation that is typically observed when fragile quantum systems are exposed to interactions with an environment. Due to the complexity of such systems, their behaviour cannot be captured by conventional simulations and require the use of so-called quantum simulators: simulators that are in themselves quantum systems and capture the physical interactions and dynamics of interest. Here, we will be in a unique position to explore the phase space of this many-body quantum simulator through spin control and Hamiltonian engineering techniques. Using the diamond surface spins, we aim to reveal spin thermalisation dynamics and many-body effects in complex spin systems.