Spin Bath of a Central Spin System in Diamond: Polarization and Coherent Control

****非技术摘要****在量子水平上控制和操纵自然是理论和实验物理学面临的最大挑战之一。量子物理学与信息科学的结合使得使用量子系统来执行传统系统无法实现的复杂计算和任务成为可能。量子信息科学面临的最重要的挑战是可靠地控制一个可扩展的量子系统，它提供了构建量子设备的能力，同时避免退相干（导致量子特性丧失的过程）。这个项目的重点是研究一个小的量子系统与一个更大的环境相互作用的退相干，其特征在一定程度上是可控的。目标是实现对退相干的更深入的物理理解。改变环境特性的能力对于更好地理解退相干是至关重要的，退相干是一种复杂的多体非平衡量子现象。反过来，更好的理解可能会导致减轻退相干和改进量子器件的技术。该项目将专注于一个系统，金刚石中的氮空位色中心，它已经成为一个非常有前途的量子设备，用于计算，磁传感和生物成像。该项目将在一个令人兴奋的多学科研究领域培养一名博士后。本研究项目得到材料研究部和物理部的支持。****技术摘要****本项目的目的是通过具有可变和可控特性的自旋浴来研究中心自旋的退相干。该项目将重点研究金刚石纳米晶体中的电子自旋浴及其对氮空位（NV）色心的影响，以获得更深入的物理理解，并有可能导致实际应用。对退相干机制的充分理解的理论和实验努力受到动力学非常复杂的阻碍。操纵介观槽的能力将被用来对中心自旋问题进行系统的研究。具体来说，将开发和实验测试使环境与中心自旋解耦、重新聚焦其内部演化以及使环境自旋极化的方案。控制和极化技术的潜在应用范围从精密测量和生物成像到量子通信和计算。例如，浴槽的控制和极化不仅可以提高最近提出的基于nv的磁传感器的灵敏度，而且还允许使用浴槽本身作为达到海森堡极限灵敏度的手段。该计划还将为凝聚态物理、纳米科学、光学成像技术和量子信息科学以及表面科学和生物成像等潜在应用领域的博士后提供跨学科培训。本研究项目得到材料研究部和物理部的支持。

****NON-TECHNICAL ABSTRACT****Controlling and manipulating nature at the quantum level is one of the greatest challenges facing both theoretical and experimental physics. The combination of quantum physics with information science has made possible the use of quantum systems to perform calculations and tasks of a complexity unattainable by systems that behave classically. The most important challenge facing quantum information science is to reliably control a scalable quantum system, which provides the ability to build quantum devices, while staving off decoherence (the process that leads to the loss of the quantum properties). The focus of this project is to study decoherence of a small quantum system interacting with a larger environment, whose characteristics are in part under control. The goal is to achieve a deeper physical understanding of decoherence. The ability to vary the environment's properties is critical to achieve a better understanding of decoherence, which is a complex many-body non-equilibrium quantum phenomenon. In turn, a better understanding may lead to techniques for mitigating decoherence and to improved quantum devices. The project will focus on a system, the Nitrogen-Vacancy color center in diamond, which has emerged as a highly promising quantum device for computation, magnetic sensing and bioimaging. This project will support the training of a postdoctoral fellow in an exciting and multidisciplinary research field. This research project receives support from the Division of Materials Research and the Physics Division.****TECHNICAL ABSTRACT****The goal of this project is to study decoherence of a central spin by a spin bath with varying and controllable characteristics. The project will focus on the electronic spin bath in diamond nano-crystals and its effects on the Nitrogen-Vacancy (NV) color center, to achieve a deeper physical understanding as well as to potentially lead to practical applications. Theoretical and experimental efforts towards a full understanding of decoherence mechanisms have been hindered by the very complexity of the dynamics. The ability to manipulate the mesoscopic bath will be exploited to perform a systematic study of the central-spin problem. Specifically, schemes for decoupling the environment from the central spin, for refocusing its internal evolution as well as for polarizing the environment spins will be developed and tested experimentally Potential applications of the control and polarization techniques range from precision measurement and bio-imaging to quantum communication and computation. For example, control and polarization of the bath would not only improve the sensitivity of recently proposed NV-based magnetic sensors, but also allow using the bath itself as a means to achieve sensitivity at the Heisenberg limit. The proposed research program will also provide interdisciplinary training of a postdoctoral fellow in condensed matter physics, nanoscience, optical imaging techniques and quantum information science, as well as in areas of potential applications, such as surface science and bioimaging. This research project receives support from the Division of Materials Research and the Physics Division.