Entangled States of Light and Atoms for Measurements Below the Standard Quantum Limit

量子力学告诉我们，物质和光都可以表现出波状或粒子状的行为。利用波的干涉（波可以相互抵消或增强）的设备，几乎可以对任何事物进行高灵敏度的测量：时间、重力、运动、电场和磁场。特别是以波干涉为基础的原子钟，是人类制造的最精确的设备，有许多重要的技术应用。时钟和其他干涉仪通过平行测量许多独立原子来增强信号。然后，设备的读数会受到测量噪声（投影噪声）的影响，就像抛硬币一样，结果并不总是正面和反面的数量相等。在这里，我们提出了一种方法来产生许多原子的相关状态（所谓的纠缠态），可以用来减少或消除投影噪声。量子力学允许人们准备一种情况，即每个硬币仍然随机显示正面或反面，但硬币的集合总是显示相同数量的正面和反面。通过演示这种状态的产生，该研究计划可以提高原子钟和其他干涉仪的精度，对计时、导航和精密测量具有重要意义。拟议的工作将通过培养研究生，并通过将本科生和优秀高中生纳入研究工作，将研究和教育目标结合起来。本项目旨在利用光学谐振器增强的集体原子-光相互作用，确定制备原子系综和光场的非经典（多体纠缠）态。这种状态可以用来提高原子钟和其他超过标准量子极限的原子干涉仪的精度。该项目的主要目标是演示一种对低于光子噪声极限的行进激光束功率的非破坏性测量，通过检测单个光子来创建薛定谔猫态或大原子系综的强自旋压缩态，并使用这些状态来操作低于标准量子的原子钟。

Quantum mechanics tells us that both matter and light can exhibit wave-like or particle-like behavior. Devices that use the interference of waves--the fact that waves can cancel each other out or enhance each other--enable highly sensitive measurements of almost anything: time, gravity, motion, or electric and magnetic fields. In particular, atomic clocks, that are based on wave interference, are the most accurate devices ever made by mankind, and have many important technological applications. Clocks and other interferometers operate by measuring many independent atoms in parallel to enhance the signal. The device readout is then subject to measurement noise (projection noise), not unlike the flipping of a collection of coins where the outcome is not always an equal number of heads and tails. Here it is proposed to develop methods to produce correlated states of many atoms (so-called entangled states) that can be used to reduce or eliminate the projection noise. Quantum mechanics allows one to prepare a situation where each coin individually still randomly shows head or tail, but the collection of coins always shows an equal number of heads and tails. By demonstrating the generation of such states, the proposed research program could boost the precision of atomic clocks and other interferometers, with significant implications for timekeeping, navigation, and precision measurements. The proposed work will unite research and educational goals by training graduate students, and by integrating undergraduate students and exceptional high-school students into the research effort. This project is aimed at the deterministic preparation of non-classical (many-body entangled) states of atomic ensembles and of light fields using collective atom-light interaction enhanced by an optical resonator. Such states can be used to improve the precision of atomic clocks and other atom interferometers beyond the standard quantum limit. The main goals of the project are to demonstrate a non-destructive measurement of the power of a traveling laser beam below the photon shot noise limit, to create Schroedinger cat states or strongly spin squeezed states of a large atomic ensemble via the detection of a single photon, and to use such states to operate an atomic clock below the standard quantum.