Collective Spin Control by Quantum Coherent Optical Feedback

这一NSF奖将支持开发一套新的工具来控制和测量其行为受量子力学支配的物理系统。该项目将把目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。基本目标是利用光作为连接遥远原子的量子巴士，从而直接控制组合的多体自旋的量子状态，而不需要单个原子直接相互作用。这将通过相干光学反馈来实现，其中光束穿过原子云以获取关于自旋的信息，然后在第二次传递中返回以相应地改变自旋量子态。衡量成功的一个重要标准是，人们可以在多大程度上减少(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计量学中有直接的应用，可能是量子通信和计算的宝贵资源。相干光反馈有可能产生压缩，这种压缩随着时间和原子云的光密度的乘积而指数地改善，相对于只线性改善的现有方案，可能会改变游戏规则。将进行实验，以确定在包括退相干、光学损失和缺陷在内的真实世界情况下的可能改进。数值模拟表明，在计划中的第一代实验中，将量子不确定性降低10倍应该是可行的。探索复杂量子系统的控制是目前跨越广泛物理学科的一项重大挑战。这一努力的动机是各种应用，从量子多体物理的模拟到量子有限的计量学和量子信息处理，所有这些应用都有一个共同的目标，即利用独特的量子属性来执行否则不可能完成的任务。该项目将为量子信息科学的知识基础做出贡献，并为这一高度交叉领域的未来科学家的培训做出贡献。学生将参与该项目的各个方面，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。每周举行一次视频会议、每年一次的研究务虚会以及共同参加会议将丰富教育经验，并加强两个机构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.