Collective Spin Control by Quantum Coherent Optical Feedback

这项NSF奖将支持开发一套新的工具来控制和测量由量子力学控制的物理系统。该项目将把当前的单原子控制方法扩展到与大量原子集合相关的多体系统。其基本目标是利用光作为量子总线来连接相距遥远的原子，从而在不需要单个原子直接相互作用的情况下直接控制组合的多体自旋的量子态。这将通过相干光反馈来实现，其中光束穿过原子云以获取有关自旋的信息，然后在第二次传递中返回以相应地转换自旋量子态。衡量成功的一个重要标准是人们能在多大程度上减小（挤压）多体自旋的基本量子不确定性。自旋压缩在量子传感和量子计量中有直接的应用，可能是量子通信和量子计算的宝贵资源。相干光反馈有可能产生压缩，随着原子云的时间和光密度的乘积呈指数级提高，并且相对于现有的仅线性提高的方案可能是一个游戏规则改变者。实验将进行，以确定可能的改进在现实世界的情况下，包括退相干，光学损耗和缺陷。数值模拟表明，在计划的第一代实验中，量子不确定性降低十倍是可行的。对复杂量子系统的控制的探索是目前在广泛的物理学科中追求的一个巨大挑战。这项工作的动机是应用范围从量子多体物理的模拟到量子有限计量和量子信息处理，所有这些都有一个共同的目标，即利用独特的量子特性来执行否则不可能完成的任务。该项目将有助于建立量子信息科学的知识库，并在这个高度跨学科的领域培养未来的科学家。学生将参与项目的各个方面，包括教育、研究和成果的传播。该项目将成为美国国家科学基金会支持的量子信息与控制中心的基石，该中心位于亚利桑那大学光学科学学院和新墨西哥大学物理与天文学系。每周的视频会议，每年的研究静修，以及共同参加会议，将丰富两所大学的教育经验，并加强两所大学的初级和高级参与者之间的联系。

This NSF award will support the development of a new suite of tools to control and measure physical systems whose behavior is governed by quantum mechanics. The project will extend current methods for single atom control to a many-body system associated with a large collection of atoms. The fundamental goal is to use light as a quantum bus to connect distant atoms, and thus gain direct control over the quantum state of the combined many-body spin without the need for individual atoms to interact directly. This will be achieved through coherent optical feedback, wherein a light beam is passed through the atom cloud to pick up information about the spin, and then returned in a second pass to transform the spin quantum state accordingly. One important measure of success is the degree to which one can reduce (squeeze) the fundamental quantum uncertainty of the many-body spin. Spin squeezing has direct application in quantum sensing and metrology, and may be a valuable resource for quantum communication and computing. Coherent optical feedback has the potential to produce squeezing that improves exponentially with the product of time and optical density of the atom cloud, and could be a game changer relative to existing schemes that improve only linearly. Experiments will be performed to determine the possible improvement in a real-world situation that includes decoherence, optical losses and imperfections. Numerical simulation suggest that a factor of ten reduction in quantum uncertainty should be feasible in the planned first generation experiment.The quest for control of complex quantum systems is a grand challenge currently pursued across a broad spectrum of physics disciplines. The effort is motivated by applications that range from the simulation of quantum many-body physics to quantum-limited metrology and quantum information processing, all of which share the goal of harnessing uniquely quantum properties to perform tasks that are not otherwise possible. This project will contribute to the knowledge base of quantum information science, and to the training of future scientists in this highly interdisciplinary field. Students will be involved in all aspects of the project, including education, research, and the dissemination of results. The project will become a cornerstone of the NSF supported Center for Quantum Information and Control, co-located at the University of Arizona College of Optical Science and the University of New Mexico Department of Physics and Astronomy. Weekly video conferencing, an annual research retreat, and joint participation in conferences will enrich the educational experience and strengthen the connections between junior and senior participants at both institutions.