Waveguide QED: Photon Correlations in Strongly Coupled Open Systems

波导 QED：强耦合开放系统中的光子相关性

• 批准号: 1404125
• 负责人: Harold Baranger
• 金额: $ 22.5万
• 依托单位: Duke University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-09-15 至 2017-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1404125&HistoricalAwards=false
• 关键词: Waveguide; QED; Photon; Correlations; Strongly

Correlations among photons are typically very weak: because photons do not interact with each other, the position of one photon does not depend on the position of another photon. However, if 'matter' is present with which the photons strongly interact, the matter mediates an effective interaction between the photons-- the first photon strongly affects the matter which then affects the second photon-- that then leads to photon-photon correlation. The matter can take a wide variety of forms, such as atoms, quantum dots, or superconducting qubits. Interactions in one dimension (1D) are particularly interesting since the photons cannot miss each other which often leads to enhanced correlations. Interest in these quantum optics phenomena in one dimension, dubbed 'waveguide Quantum Electrodynamics (QED)', or "waveguide QED",, has rapidly grown in recent years, driven notably by the fact that several such experimental systems can now be made with relatively strong interactions. Examples include tapered fibers coupled to atoms, microwave transmission lines coupled to superconducting qubits, and semiconductor dielectric waveguides coupled to quantum dots. Photon correlations in multi-qubit waveguide systems will be studied. Theoretically much is now known about a single atom or qubit interacting with 1D photons, and so the time is ripe for considering photonic waveguide systems with more complex matter. First, situations in which a few two-level-systems (qubits or atoms, say) interact with 1D light will be studied with the aim of describing the specifically quantum properties of the light that can be produced (non-classical light). Then, the case of many qubits (a large amount of matter) will be considered with the idea that new phases of the light/matter system may be possible. Phase transitions in driven systems, called dynamical phase transitions, are receiving increasing attention; the waveguide QED system may be a way to realize different kinds of dynamical phases. The research in this project connects to several other broad fields. First, nanophotonic devices often involve two-level systems and 1D modes as building blocks. The new physical effects studied here will lead to a better understanding of such elements and may lead to qualitatively new devices. Second, the proposed structures in their superconducting qubit/microwave version constitute quantum meta-materials, a rapidly developing offshoot of the enormous interest in meta-materials generally in recent years. Third, quantum networks for quantum information purposes involve elements that look exactly like the waveguide QED systems studied here. The subject of this research is the correlations among photons in a waveguide caused by their interaction with discrete quantum objects, such as atoms, quantum dots, or qubits. Photon correlations caused by strong light-matter interaction have been studied extensively in the context of relatively closed cavities. In contrast, one-dimensional (1D) waveguides are quantum open systems, in some of which, nevertheless, it may soon be possible to achieve strong coupling to atoms or qubits. In this theoretical work photon correlations in multi-qubit waveguide systems will be investigated. Specifically, three areas will be studied. First, nonclassical light and time delay for few qubit systems will be studied. The photon correlations (coherences) will be calculated for several few qubit situations involving up to 10 two-level or three-level systems. An immediate result will be the change in the properties of the non-classical light generated as a function of number of qubits - non-classical features are expected to be enhanced, though the interplay with interference effects may be complicated. Three-level systems introduce a new aspect: time-delay. The use of this for enhancing interaction or interference effects (interferometry) will be evaluated. Second, for many qubit systems, the question of whether dynamical phase transitions can produce new states of light will be studied. An infinite system with sparse periodic, disordered, or dense atoms or qubits brings in the possibility of a new state of light. Since the system is necessarily driven, this would involve a dynamical phase transition. Whether such a transition can take place in a waveguide QED system will be evaluated. Finally, quantum optics phenomena with DC electrical transport will be studied. Electromagnetic radiation along a chain of Josephson junctions coupled to a superconducting qubit is a new waveguide QED system. If time permits, the possibility of probing the system by electrical transport through a weakly coupled probe junction, thus revealing the quantum optics properties, will be investigated. Several methods will be used to tackle these problems. Tasks 1 and 3 can be started with exact methods that were developed previously, and then will be continued with numerical propagation of pulses. Both the few and many qubit problems will be approached with a slave-boson mean field theory and Keldysh quantum field theory. The comparison with the exact methods in the few qubit cases will provide an important cross-check.

光子之间的相关性通常非常弱：因为光子彼此不相互作用，一个光子的位置不依赖于另一个光子的位置。然而，如果存在与光子强烈相互作用的“物质”，则物质介导光子之间的有效相互作用-第一个光子强烈影响物质，然后影响第二个光子-然后导致光子-光子相关。物质可以采取各种各样的形式，如原子、量子点或超导量子比特。一维（1D）的相互作用特别有趣，因为光子不会相互错过，这通常会导致增强的相关性。近年来，人们对这些一维量子光学现象的兴趣迅速增长，被称为“波导量子电动力学（QED）”或“波导QED”，这主要是由于几个这样的实验系统现在可以用相对较强的相互作用来制造。例子包括耦合到原子的锥形光纤，耦合到超导量子位的微波传输线，以及耦合到量子点的半导体介电波导。研究了多量子比特波导系统中的光子关联。从理论上讲，现在已经知道了很多关于单个原子或量子比特与一维光子相互作用的知识，因此考虑具有更复杂物质的光子波导系统的时机已经成熟。首先，我们将研究一些二能级系统（比如量子比特或原子）与一维光相互作用的情况，目的是描述可以产生的光（非经典光）的特定量子特性。然后，将考虑许多量子比特（大量物质）的情况，并考虑光/物质系统的新相位可能是可能的。被驱动系统中的相变，称为动力学相变，正受到越来越多的关注，波导QED系统可能是实现不同类型的动力学相位的一种方式。该项目的研究与其他几个广泛的领域有关。首先，纳米光子器件通常涉及两级系统和1D模式作为构建块。这里研究的新的物理效应将导致更好地理解这些元素，并可能导致新的设备质量。其次，所提出的超导量子比特/微波版本的结构构成了量子超材料，这是近年来对超材料的巨大兴趣的一个迅速发展的分支。第三，用于量子信息目的的量子网络涉及与本文研究的波导QED系统完全相似的元件。本研究的主题是波导中光子与离散量子物体（如原子、量子点或量子比特）相互作用所引起的光子之间的相关性。在相对封闭的腔中，由强光-物质相互作用引起的光子关联已经被广泛研究。相比之下，一维（1D）波导是量子开放系统，尽管如此，在其中一些系统中，可能很快就有可能实现与原子或量子位的强耦合。在这篇理论工作中，我们将研究多量子位波导系统中的光子关联。具体而言，将研究三个领域。首先，我们将研究少量子比特系统的非经典光和时间延迟。光子相关性（相干性）将被计算的几个少数量子比特的情况下，涉及多达10个二能级或三能级系统。一个直接的结果将是作为量子比特数量的函数产生的非经典光的性质的变化-非经典特征预计将得到增强，尽管与干涉效应的相互作用可能是复杂的。三电平系统引入了一个新的方面：时滞。将评估使用这种方法来增强相互作用或干涉效应（干涉测量法）。其次，对于许多量子比特系统，动态相变是否可以产生新的光态的问题将被研究。一个具有稀疏周期性、无序或密集原子或量子比特的无限系统带来了新的光状态的可能性。由于系统必须被驱动，这将涉及动态相变。这种转变是否可以发生在波导QED系统将进行评估。最后，将研究直流电输运的量子光学现象。电磁辐射沿着耦合到超导量子比特的约瑟夫森结链是一种新的波导QED系统。如果时间允许，我们将研究通过弱耦合探测结的电输运探测系统的可能性，从而揭示量子光学性质。将使用几种方法来解决这些问题。任务1和任务3可以用以前开发的精确方法开始，然后继续进行脉冲的数值传播。无论是少数和许多量子比特的问题将接近一个从玻色子平均场理论和凯尔迪什量子场论。在少数量子位情况下与精确方法的比较将提供重要的交叉检查。