Spin Polarization and Transport at the Nanoscale

与金刚石缺陷（氮空位色心）相关的量子自旋可用于感应磁场，具有前所未有的灵敏度和空间分辨率。这些新型传感器可以在纳米尺度和环境条件下阐明材料和生物分子的结构和动力学。这些传感器成功的一个关键因素是了解它们的环境（由其他钻石自旋缺陷组成），这些环境通常会破坏它们的特性。本项目的重点不仅是了解氮空位中心与其自旋环境的相互作用，而且是将这些自旋转化为资源。这一目标将通过研究环境自旋特性和动力学，并通过开发控制技术来操纵和测量它们来实现。反过来，更好地理解自旋系统和新的控制技术将产生用于传感和生物成像的改进的量子器件。此外，在纳米尺度上探索自旋动力学的能力，通过在金刚石中使用氮空位中心开辟了一种可能性，将推进对这种复杂的多体非平衡量子现象的认识，并对更广泛的学科产生影响，包括量子计算和MRI。该项目将支持研究生研究人员在一个令人兴奋的多学科研究领域的培训。本研究计划将探索自旋极化在纳米尺度上的基础物理和潜在应用，并在理论和实验之间发挥协同作用。该项目利用金刚石中的氮空位（NV）中心作为周围电子和核自旋环境中局部自旋极化的种子和传感器。目标是首先通过NV中心的光学冷却及其与自旋浴的热接触实现有效的极化积累；其次，研究介观自旋环境下的后续动力学（极化输运）。由于NV探测的高空间分辨率和新的材料工程技术，这些单自旋系统上的现象将能够在纳米尺度上进行研究。该计划的智力价值在于通过实验和理论模型来阐明自旋扩散现象，研究传统磁共振技术以前无法达到的尺度。自旋扩散是一个复杂的量子多体过程，它是磁共振实验中的退相干和动态极化等现象的基础。此外，利用工程材料，将研究如何通过准一维电子自旋浴来促进远距离NV中心之间的相干自旋输运。这些研究将对不同学科产生更广泛的影响，从量子计算和计量学到通过动态核极化（DNP）的蛋白质传感。金刚石中的电子自旋可以用作自旋线，在NV中心的量子寄存器之间传递量子信息。偏振自旋浴可以通过NV中心来改进量子计量，通过产生纠缠态来实现更长的相干时间和海森堡极限灵敏度。对自旋扩散的新见解-特别是自旋扩散势垒-将导致DNP策略的改进，DNP是核磁共振测定蛋白质结构的一种流行技术。超极化纳米金刚石本身可以用作极化剂，溶解在感兴趣的生物样品中以提高灵敏度。

Quantum spins associated with defects in diamond (Nitrogen-Vacancy color centers) can be used to sense magnetic fields with an unprecedented combination of sensitivity and spatial resolution. These novel sensors could elucidate the structure and dynamics of materials and biomolecules at the nano-scale and ambient conditions. A critical ingredient to the success of these sensors is the understanding of their environment (composed of other diamond spin defects) that usually spoil their properties. The focus of this project is not only to understand the interaction of Nitrogen-Vacancy centers with their spin environment, but also to turn these spins into a resource. This goal will be accomplished by studying the environmental spin properties and dynamics and by developing control techniques to manipulate and measuring them. In turns, a better understanding of the spin system and novel control techniques will yield improved quantum devices for sensing and bio-imaging. In addition, the ability to explore spin dynamics at the nano-scale, a possibility opened by the use of Nitrogen-Vacancy centers in diamond, will advance the knowledge of this complex, many-body non-equilibrium quantum phenomenon and have impact in broader disciplines, including quantum computation and MRI. This project will support the training of graduate student researchers in an exciting and multidisciplinary research field. This research program will explore fundamental physics and potential applications of spin polarization at the nanoscale, with a synergistic interplay between theory and experiment. The project exploits the Nitrogen-Vacancy (NV) center in diamond as a seed and sensor of local spin polarization in the surrounding electronic and nuclear spin environment. The goals are to first achieve efficient polarization buildup via optical cooling of the NV center and its thermal contact with the spin bath; and second, to investigate the subsequent dynamics (polarization transport) in the mesoscopic spin environment. Thanks to high spatial resolution of NV detection and to novel material engineering techniques, these phenomena on single-spin systems, will be able to be studied at the nano-meter scale. The intellectual merit of the program lies in elucidating, via experiments and theoretical models, the phenomenon of spin diffusion, investigating scales not previously accessible to conventional magnetic resonance techniques. Spin diffusion is a complex quantum many-body process, which underlies, for example, decoherence in magnetic resonance experiments as well as dynamic polarization. In addition, by using engineered materials, how to promote coherent spin transport between distant NV centers, mediated by a quasi-one dimensional bath of electronic spins, will be studied. These studies will have a broader impact in different disciplines, from quantum computation and metrology, to protein sensing via dynamic nuclear polarization (DNP). Electronic spins in diamond can be used as spin wires to transfer quantum information between quantum registers located at the NV centers. A polarized spin bath can be used to improve quantum metrology via NV centers, by achieving longer coherence time and Heisenberg-limited sensitivity via the creation of an entangled state. Novel insight into spin diffusion -especially at the spin diffusion barrier- would lead to improved strategies for DNP, a popular technique in protein structure determination with NMR. Hyper-polarized nano-diamonds could themselves be used as polarizing agents, dissolved in bio-samples of interest for improved sensitivity.