Quantum Coherence and Entanglement with Atomic, Molecular and Optical Systems

这项研究计划旨在了解和控制原子、分子和光学(AMO)系统中的量子相干和纠缠态。复合子系统的纠缠态是不能用其子系统的单独的真实描述来描述的状态。纠缠态是量子信息处理研究的核心，这不仅为量子计算机或量子密码学等新技术的发展指明了方向，还可能加深对量子力学的理解。AMO物理学的一项重要发展是研究集体原子系综变量，它提供了气体或蒸汽中微观自由度(如单光子波包)和宏观自由度(如电子、振动或旋转自由度)之间的接口。目前正在研究两个主题：(1)在Rb蒸气基态中集体电子激发的介观纠缠；(2)探索一种用于量子光学的新平台--空芯光子晶体光纤。主题(1)旨在将最近在单光子和双光子水平上关于原子系综和光场的数态纠缠的实验扩展到5到20光子水平。这需要在光子数分辨检测和高阶场统计矩的测量方面取得最先进的进展。这验证了一种假设，即纠缠即使在宏观世界中也是自然界的一个强大特征，但随着激发数变得越来越大，从技术上来说，检测它变得越来越困难。在某个高激发数下，量子理论要么变得无关紧要，要么崩溃。该实验有几个独特的方面：i)一种新型的光子数分辨探测器--背光漂移硅光电倍增管--被用来测量斯托克斯光脉冲，从而在5-20个激发数区域产生非高斯原子系综纠缠。Ii)为了验证纠缠，研究人员正在开发平衡的零差关联，使用一种更实用的方案，基于ccd相机，而不是最初设想的多个分束器。主题(2)将研究扩展到一个新的有前途的领域：空芯光子晶体光纤(HC-PCF)。该研究小组将与巴斯大学的一个研究小组合作，对充锶、充氢和充氙的HC-PCF进行探索性研究。长光程和严格可控的光学约束使这些系统在超低强度非线性量子光学方面具有很好的应用前景，包括创建超宽带梳状光谱场、产生光子对、四模光学纠缠、原子-光场纠缠等。这项研究将有助于更广泛地理解量子纠缠及其测量。这可能会影响对量子物理基础以及量子信息科学的研究。在项目的规划中，研究生和本科生的教育是首要的。本科生将通过REU项目参与进来。该项目的重要合作方面包括与俄勒冈大学Steven van Enk教授的理论小组的密切互动，与英国巴斯大学F.Benabid教授在HC-PCF方面的实验合作，以及与德国Garching的Max Planck研究所的H.-G.Moser在光子数分辨探测器方面的技术合作。国际物理学会参与了各种外展工作，包括公开讲座、新课程开发和教科书编写，以努力将物理带给更广泛的受众。他通过暑期学校和研究合作参与了国际推广活动。而且，PI是俄勒冈大学光学中心的创始主任，这是一个涉及物理和化学的教职员工和学生的协同中心。

This research program aims to understand and control quantum coherence and entangled states in atomic, molecular, and optical (AMO) systems. An entangled state of a compound subsystem is one that cannot be described in terms of separate realistic descriptions of its subsystems. Entangled states are central in studies of quantum information processing, which in addition to showing the way towards new technologies, such as quantum computers or quantum cryptography, may lead to deeper understanding of quantum mechanics. An important development in AMO Physics is the study of collective atomic-ensemble variables, which provide an interface between microscopic degrees of freedom, such as single-photon wave packets, and macroscopic degrees of freedom, such as electronic, vibrational or rotational, in a gas or vapor. Two themes are being pursued: (1) Mesoscopic-level entanglement of collective electronic excitation in the ground states of rubidium vapor, and (2) Exploration of a new platform--hollow core photonic crystal fibers--for use in quantum optics. Theme (1) seeks to extend recent experiments on number-state entanglement of atomic ensembles and optical fields at the one- and two-photon level to the 5-to-20 photon level. This requires state-of-the-art advances in both photon-number-resolving detection and in the measurement of higher-order field statistical moments. This tests the hypothesis that entanglement is a robust feature of nature even in the macroscopic world, but that detecting it becomes progressively more difficult technically as the excitation number becomes large. At some high excitation number, the quantum theory could either become irrelevant or break down. The experiment has several unique aspects: i) A new type of photon-number-resolving detector--a back-illuminated drift silicon photomultiplier--is being used to measure Stokes light pulses, thereby creating non-Gaussian atomic-ensemble entanglement in the 5-20 excitation-number regime. ii) To verify entanglement the researchers are developing balanced homodyne correlation, using a more practical scheme based on a CCD camera rather than multiple beam splitters as originally conceived. Theme (2) extends the research into a new promising area: hollow-core photonic crystal fibers (HC-PCF). In collaboration with a group at Bath University, the research team will undertake exploratory studies of rubidium-filled, hydrogen-filled, and xenon-filled HC-PCF. The long path lengths and tight, controlled optical confinement make these systems promising for ultralow-intensity nonlinear quantum optics, including creation of ultrawide-band comb-spectrum fields, photon pair generation, four-mode optical entanglement, atom-field entanglement, and others. The research will contribute broadly to the understanding of quantum entanglement and its measurement. This may impact studies of the foundations of quantum physics as well as quantum information science. Education of graduate students and undergraduate students is foremost in the planning of the project. Undergraduate students will be involved through REU programs. Important collaborative aspects of the project include close interaction with the theory group of Prof. Steven van Enk at the University of Oregon, experimental collaboration with Prof. F. Benabid at Bath University in England on HC-PCF, and technical collaboration with H.-G. Moser at Max Planck Institute in Garching, Germany on photon-number-resolving detectors. The PI is involved in various outreach efforts, including public lectures, new course development and textbook authoring, in an effort to bring physics to a wider audience. He is involved in international outreach through summer schools and research collaborations. And, the PI was founding Director of the Oregon Center for Optics at the UO, a synergistic center involving faculty and students from physics and chemistry.