Superconducting Circuits and Macroscopic Quantum States of Light and Sound

该奖项支持理论凝聚态物理的研究和教育。微波电路设计的最新进展涉及由超导体制成的类似晶体管的元件，这使得超导电流与微波强烈相互作用的能力得以实现。在足够低的温度下，超导体中的超电流可以不耗散地导电。超导态涉及大量电子的集体行为，这些电子在一起可以表现出原子和分子世界中典型的量子力学态的特性，尽管超导体本身是一个宏观物体。初步研究表明，由此产生的微波具有固有的低噪声，有点类似于激光。这样的微波源可能对量子通信有用。该项目旨在从理论上理解这些强光荷相互作用产生的微波的本质。PI将与实验人员密切合作。在一个相关的推力中，PI将研究一个混合系统，其中超导晶体管元件将微波与纳米级机械振动线耦合。预计这种耦合将导致微波和耦合机械振动的低固有噪声。这种振动纳米线装置可以实现超灵敏力显微镜的研制。这两个项目的总体目标是发展对如何产生稳态、大振幅微波和纳米力学运动的理解，这些运动具有明显的量子力学特性，如超低振幅噪声，也被称为“量子压缩”。参与该项目的研究生和高级本科生将接受理论凝聚态物理方面的培训。学生们将从同事Rimberg教授的实验室直接获得实验结果中受益，并将帮助解释实验。该奖项支持理论研究和教育，以推进对一类超导电路系统的理解，这些系统将微波光子与库珀对输运和纳米机械运动强烈耦合。该活动包括两个超导电路项目。其中一个项目将发展库珀对激光的综合理论，特别是阐明产生的微波腔光子的量子性质，并对最近和计划中的实验数据进行建模。另一个项目将开发一个相关的微波腔-库珀对电路系统的理论，该系统包括一个纳米机械谐振器，也正在实验中实现。该系统实现了微波腔光子与纳米力学能量子-声子之间的超强耦合。该项目将特别解决涉及大平均声子数的机械谐振器的明显量子态的产生。理论研究将补充达特茅斯大学的同事亚历克斯·伦伯格教授的平行实验工作，也得到了美国国家科学基金会的支持。该项目的目标是更好地理解如何产生稳定的微波量子源和涉及大平均光子和声子数的机械量子态。鲁棒的、可调谐的量子微波源可能会在量子通信中得到应用，而稳定的、连续产生的机械量子态可能会在超灵敏的位置检测中得到应用。该奖项支持培养一名研究生，以及参与理论凝聚态物理研究的高级本科生，在许多物体理论、介观量子物理、非线性动力学、量子光学和计算物理等领域获得专业知识。学生们也将有机会运用他们的理论模型来帮助解释Rimberg教授小组的实验数据。

NONTECHNICAL SUMMARYThis award supports research and education in theoretical condensed matter physics. Recent developments in the design of microwave circuits involving transistor-like elements made of superconductors have resulted in the ability to make electrical supercurrents interact strongly with microwaves. At sufficently low temperature, supercurrents in superconductors carry electricity without dissipation. The superconducting state involes the collective behavior of a large of electrons that together can exhibit properties of quantum mechanical states typical of the world of atoms and molecules even though the supercondutor itself is a macroscopic object. Preliminary work suggests that the resulting generated microwaves can be inherently low noise, somewhat akin to a laser. Such microwave sources may be useful for quantum communication purposes. The PI aims to develop a theoretical understanding of the nature of the microwaves that are generated as a result of these strong light-charge interactions. The PI will work in close collaboration with experimentalist. In a related thrust the PI will investigate a hybrid system where a superconducting transistor element couples microwaves with a nanoscale, mechanical vibrating wire. It is expected that this coupling will result in low inherent noise for the microwaves and coupled mechanical vibrations. This kind of vibrating nanowire device may enable the development of an ultasensitive force microscope. An overall goal of these two projects is to develop an understanding of how to generate steady-state, large amplitude microwave and nanomechanical motions that have manifestly quantum mechanical properties such as ultralow amplitude noise, otherwise known as "quantum squeezing." A graduate student and advanced undergraduate students involved in the project will receive training in theoretical condensed matter physics. The students will benefit from having direct access to experimental results from colleague Prof. Rimberg's lab, and will help in the interpretation of the experiments. TECHNICAL SUMMARYThis award supports theoretical research and education concerned with advancing understanding of a class of superconducting circuit systems that strongly couple microwave photons to Cooper pair transport and to nanomechanical motion. The activity comprises two superconducting circuit projects. One project will develop a comprehensive theory of the Cooper pair laser, in particular elucidating the quantum nature of the generated microwave cavity photons and modeling the data from recent and planned experiments. The other project will develop the theory for a related microwave cavity-Cooper pair circuit system that includes a nanomechanical resonator, also being realized in experiment. This recently proposed system achieves ultra strong coupling between the microwave cavity photons and nanomechanical energy quanta--phonons. The project will in particular address the generation of manifestly quantum states of the mechanical resonator involving large average phonon number. The theoretical investigation will complement a parallel experimental effort by Dartmouth colleague Prof. Alex Rimberg, also supported by the NSF. The goal of the project is to provide a better understanding of how to generate steady, quantum sources of microwaves and mechanical quantum states involving large average photon and phonon numbers. Robust, tunable sources of quantum microwaves may find application in quantum communication, while steady, continuously generated mechanical quantum states may find use in ultra sensitive position detection.This award supports the training of a graduate student, as well as advanced undergraduate students involved in the research in theoretical condensed matter physics, gaining expertise in such areas as many body theory, mesoscopic quantum physics, nonlinear dynamics, quantum optics, and computational physics. The students will also have opportunities to apply their theoretical models to help explain experimental data from Prof. Rimberg's group.