Atomic Ensembles Entangled by Light for Measurements Below the Standard Quantum Limit

原子系综的纠缠态有可能克服量子测量中的各种限制，包括与对一组独立粒子的测量相关的所谓标准量子限制。为了实现多体系统中的纠缠，将使用光学谐振腔内冷原子的内态，这些原子与激光强耦合。腔内的光子充当远距离原子之间的信使，可以用来诱导有效的依赖于状态的长程原子-原子相互作用。这些相互作用可以被用来重新分配量子噪声，从而提高原子钟和原子干涉仪的信噪比(自旋压缩)。在这个项目中，我们实现了一种改进的自旋压缩方法，它允许人们在保持光介导的原子-原子相互作用的同时，将出射的光从原子中分离出来。这种新的方法不仅提供了比以前更强的自旋压缩，而且还可以在介观原子系综中产生非高斯纠缠态甚至薛定谔猫态。此外，利用原子与光谐振腔模式的强相互作用，我们希望展示各种新型量子光学器件，包括单光子全光开关、色散光子数态滤光器和两个光子之间的确定性量子门。物理学的一个主要前沿是量子力学多体系统的控制。这种控制将使存储和处理量子信息的新型设备成为可能，提高基本精度测量，并增强和深化我们对多体量子物理关键概念的理解。特别令人感兴趣的是对原子钟等精密系统的量子控制。原子钟是人类有史以来制造的最精确的设备，有许多重要的技术应用，包括全球定位系统和电信网络。这一研究计划可以显著提高光学跃迁原子钟的精度，超越目前的限制，并使许多与精确计时能力相关的新技术成为可能。该项目将培养研究生和本科生。优秀的高中生将被纳入这项研究工作。努力吸纳代表人数不足的少数民族学生。

Entangled states of atomic ensembles have the potential to overcome various limits in quantum measurements, including the so-called standard quantum limit associated with measurements on a collection of independent particles. To realize entanglement in a many-body system, internal states of cold, trapped atoms that are strongly coupled to laser light inside an optical resonator will be used. The photons inside the cavity act as messengers between distant atoms, and can be used to induce effective state-dependent long-range atom-atom interactions. These interactions, in turn, can be utilized to redistribute quantum noise so as to enhance the signal-to-noise ratio of atomic clocks and atom interferometers ("spin squeezing"). In this project we implement a modified spin squeezing method that allows one to disentangle the outgoing light from the atoms while maintaining the light-mediated atom-atom interaction. This new method provides not only much stronger spin squeezing than previously possible, it also enables the generation of non-Gaussian entangled states and even Schroedinger cat states in mesoscopic atomic ensembles. Furthermore, using the strong interaction between an atom and a mode of the optical resonator, we hope to demonstrate a variety of novel quantum optical devices, including a single-photon all-optical switch, a dispersive photon-number-state filter, and a deterministic quantum gate between two photons.A major frontier of physics is the control of quantum mechanical many-body systems. Such control will enable novel devices for storing and processing quantum information, improve fundamental precision measurements, and enhance and deepen our understanding of key concepts of many-body quantum physics. Of particular interest is the quantum control of precision systems such as atomic clocks. Atomic clocks are the most accurate devices ever made by mankind, and have many important technological applications, including the Global Positioning System and telecommunication networks. This research program could significantly improve the precision of optical-transition atomic clocks beyond current limits, and enable many new technologies linked to the ability to precisely keep time. The project will train graduate students and undergraduate students. Exceptional high-school students will be integrated into the research effort. Efforts are made to include underrepresented minority students.