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，包括与测量一组独立粒子相关的所谓标准量子限制。为了在多体系统中实现纠缠，将使用与光学谐振器内的激光强耦合的冷的被捕获原子的内部状态。腔中的光子作为远距离原子之间的信使，可以用来诱导有效的依赖态的长程原子-原子相互作用。反过来，这些相互作用可以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，我们实现了一个修改的自旋压缩方法，允许一个解开从原子的出射光，同时保持光介导的原子-原子相互作用。这种新的方法不仅提供了比以前可能的更强的自旋压缩，它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，利用原子与光腔模之间的强相互作用，我们还有望实现各种新型的量子光学器件，包括单光子全光开关、色散光子数态滤波器以及双光子间的确定性量子门。量子力学多体系统的控制是物理学的一个重要前沿。这种控制将使存储和处理量子信息的新设备成为可能，提高基本的精确测量，并增强和加深我们对多体量子物理学关键概念的理解。特别令人感兴趣的是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，并具有许多重要的技术应用，包括全球定位系统和电信网络。这项研究计划可以大大提高光跃迁原子钟的精度，使其超越目前的限制，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。特殊的高中学生将被纳入研究工作。 努力将代表性不足的少数民族学生包括在内。

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.