Physics and Applications of Cooperative Effects in Nonlinear and Quantum Optics

密集的原子集合可以表现出与稀释样品中的集体现象根本不同的现象。一个例子是超辐射，其中一组原子集体与特定的光场相互作用。虽然这个话题很早就被认识到，但在过去几年里变得越来越重要。许多基础研究领域（例如量子信息科学）和应用领域（例如精确原子钟的构建）现在都利用了密集系综的集体特性。密度效应可能是有害的。增加原子之间的相互作用强度可以破坏原子对外部刺激的相干响应，这对于量子计算机或精确时钟来说是必需的。该项目的目标是（i）发现并理解密度相关的集体效应及其后果，（ii）研究减轻或隔离效应的方法，以改善对系综的实验控制，以及（iii）研究此类效应可以实现新技术的各种方式。将研究有关合作介质中集体效应的基本问题，例如：超辐射效应取决于密度或光学深度吗？交换互动的具体作用是什么？驱动型协作系统有何特别之处？超辐射率是否完全由成对相关性描述，哪些系统需要其他近似值？为了实现这些目标，将开发新的分析和数值方法。此外，该项目将研究的特殊效应包括诱导和自发的集体线位移、自旋和光场“挤压”以及纠缠。此外，动态卡西米尔效应的统计和非线性将与超辐射系统的集体效应进行比较。大多数这些项目将包括与实验工作的合作。

A dense collection of atoms can display collective phenomena which are fundamentally different from those in dilute samples. An example is super-radiance, where an ensemble of atoms collectively interacts with a specific light field. While recognized long ago, this topic has gained importance over the last few years. Many areas of fundamental research, such as quantum information science, and of applications, such as the construction of accurate atomic clocks, now utilize collective properties of dense ensembles. Density effects can be detrimental. Increasing the interaction strength between atoms can destroy the coherent response of the atoms to external stimuli, which is necessary for quantum computers or precise clocks. The goal of this project is to (i) find and understand density-dependent collective effects and their consequences, (ii) to investigate methods to either mitigate or isolate the effects in a way to improve experimental control of the ensembles, and (iii) to research the various ways in which such effects can enable new technologies. Basic questions will be studied regarding collective effects in cooperative media, such as: Do super-radiant effects depend on density or optical depth? What exactly is the role of the exchange interaction? What makes driven cooperative systems special? Is super-radiance fully described by pairwise correlations, and for which systems are other approximations needed? In order to achieve these goals, new analytical and numerical methods will be developed. In addition, the particular effects that will be investigated in this project include induced and spontaneous collective line shifts, spin and light field "squeezing" and entanglement. In addition, statistics and nonlinearities of the dynamic Casimir effect will be compared to the collective effects of super-radiant systems. Most of these projects will include collaboration with experimental efforts.