Single-Photon Subradiance, Superradiance, and Emergent Cooperativity in Cold Atomic Matter

冷原子物质中的单光子次辐射、超辐射和突现协同性

• 批准号: 1606743
• 负责人: Charles Sukenik
• 金额: $ 45.85万
• 依托单位: Old Dominion University Research Foundation
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-08-15 至 2021-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1606743&HistoricalAwards=false
• 关键词: Single; Photon; Subradiance; Superradiance; Emergent

The merger of quantum optics and cold atom physics has revolutionized several areas of scientific and technical development. Quantum optics is the field of study of particles of light, photons, and their interaction with matter. Cold atom physics is the investigation of cold atoms and their interaction with light and with other matter. (Atoms can be cooled to as low a temperature as about 50 picokelvin, a thrillionth of a degree above absolute zero. For comparison, the cold near vacuum of outer space is about 3 Kelvin, and room temperature is about 300 Kelvin.) These joined scientific areas have led to improved atomic clocks, development of sensors of magnetic and electric fields, measurements of gravitational forces, and rotational motion, to name a few. At the same time, entirely new areas of practical and fundamental investigation been developed, including quantum simulations of materials and plasma physics, and the dynamic research area of quantum informatics. This project is focused on experimental and theoretical study of single-photon super radiance and sub radiance in cold atomic gases. These are emergent effects, which do not occur for single atoms by themselves, but require cooperative interactions among a group of atoms. In super radiance, light emitted from a gas of cold atoms does so at a rate much faster than from a single atom. The light also is emitted in a narrow cone and behaves like a jet of photons. In sub radiance, the converse is true; light emerges on the average in all directions, at a very slow rate, and can even be stored for a long period of time in the gas. These fundamental quantum optical processes are accompanied by a shift of the frequency (or wavelength) and loss of the purity of the color of the emitted light. As such, these effects can have a negative influence on the performance of atomic clocks or other precision sensors. Thorough understanding of super and sub radiance, one of the main goals of this project, is thus essential to optimizing the operation of these devices. On the other hand, it is possible to use these effects to advantage to form the basis of a single photon memory for light. In this case, a photon is taken up in a super radiant state, and quickly transferred to a long lived sub radiant configuration. At a later controllable time the atomic gas can be switched back to a super radiant state, in which the stored photon is reemitted into its original mode. The main scientific focus of this project is to study and understand the phenomenology of single photon super and sub radiance in cold atomic gases, and to learn about the impact of these processes on quantum sensors, and possible applications to single photon quantum memories. In the project, a dense and cold sample of cold rubidium atoms is optically prepared and interrogated by a narrow-band and near-resonance probe beam. The atomic sample is elliptical with large aspect ratio, and is typically optically excited along the long axis. This geometry has been shown theoretically to lead to an enhanced collective Lamb frequency shift in the forward scattered light. The probe beam is prepared as a temporally short pulse for time resolved studies and is considerably longer and spectrally narrower for frequency shift measurements. Enhanced and rapid emission is observed in the near-forward direction, while both super radiant and sub radiant emission is studied in an off-axis configuration. In initial studies, single photon super radiance is observed; the rate for the process is found to increase linearly with increasing optical depth, characteristic of a cooperative process. A spectral shift of the resonance to lower frequency, with linear dependence on the optical depth, has also been measured. Current and developing aspects of the project include study of (a) superradiant pulse propagation effects in the dense gas. These can modify the linear cooperative scaling and limit the practical applications; (b) few-body collective effects including two-body super and sub radiance; (c) the influence of inhomogeneous broadening process, such as Doppler broadening and trap induced light shifts on mixing and controlled coupling between super and sub radiant configurations.

量子光学和冷原子物理学的结合彻底改变了科学和技术发展的多个领域。 量子光学是研究光粒子、光子及其与物质相互作用的领域。 冷原子物理学是对冷原子及其与光和其他物质相互作用的研究。 （原子可以冷却到约 50 皮开尔文的低温，即高于绝对零度的千分之一度。作为比较，外层空间接近真空的温度约为 3 开尔文，室温约为 300 开尔文。）科学领域导致了原子钟的改进、磁场和电场传感器的发展、重力测量和旋转运动等等。 与此同时，全新的实用和基础研究领域得到了发展，包括材料和等离子体物理的量子模拟，以及量子信息学的动态研究领域。 该项目专注于冷原子气体中单光子超辐射和亚辐射的实验和理论研究。 这些是突现效应，单个原子本身不会发生，而是需要一组原子之间的协作相互作用。 在超辐射中，冷原子气体发出的光的速度比单个原子快得多。 光也以狭窄的锥体形式发射，其行为类似于光子射流。 在亚光亮度下，情况正好相反；光平均向各个方向发出，速度非常慢，甚至可以在气体中储存很长一段时间。 这些基本的量子光学过程伴随着频率（或波长）的变化和发射光颜色纯度的损失。 因此，这些效应可能会对原子钟或其他精密传感器的性能产生负面影响。 因此，透彻了解超辐射率和次辐射率是该项目的主要目标之一，对于优化这些设备的操作至关重要。 另一方面，可以利用这些效应来形成光的单光子存储器的基础。 在这种情况下，光子在超辐射状态下被吸收，并迅速转移到长寿命的亚辐射配置。 在稍后的可控时间，原子气体可以切换回超辐射状态，其中存储的光子被重新发射到其原始模式。 该项目的主要科学重点是研究和理解冷原子气体中单光子超辐射和亚辐射的现象学，并了解这些过程对量子传感器的影响，以及在单光子量子存储器中的可能应用。在该项目中，通过光学方法制备了致密且冷的冷铷原子样品，并通过窄带和近共振探测光束进行询问。 原子样品是具有大纵横比的椭圆形，并且通常沿着长轴进行光学激发。 理论上，这种几何形状已被证明会导致前向散射光中的集体兰姆频移增强。 探测光束被准备为用于时间分辨研究的时间短脉冲，并且对于频移测量来说相当长且光谱更窄。 在近前方向观察到增强和快速发射，而在离轴配置中研究超辐射和亚辐射发射。在初步研究中，观察到单光子超辐射；发现该过程的速率随着光学深度的增加而线性增加，这是协作过程的特征。 还测量了共振到较低频率的光谱偏移，与光学深度呈线性相关。 该项目当前和正在发展的方面包括研究（a）稠密气体中的超辐射脉冲传播效应。这些都会修改线性协同缩放并限制实际应用； (b) 少体集体效应，包括两体超辐射和亚辐射； (c)不均匀展宽过程的影响，例如多普勒展宽和陷阱引起的光位移对超辐射配置和次辐射配置之间的混合和受控耦合的影响。