Quantum Fluctuations of the Order Parameter in Superconductors

本基金支持基础凝聚态物理的理论研究。在过去的十年里，人们对介观超导进行了大量的实验研究。目前，由于在量子计算中寻找可行的方案，对这一领域的兴趣进一步增加。到目前为止，理论上的并行工作主要集中在超导和杂化结构的平衡特性和线性响应特性上。然而，根据实验的要求，很明显需要了解远离平衡的杂化结构的性质。本研究将探索这些特性。第一个项目处理受参数激励的小约瑟夫森结电路的动态特性。驱动结系统可以进入经典或量子动态混沌状态。如果结足够小以允许电荷量子化，量子效应就变得重要。我们将探讨两个结点系统中的混沌。对这样一个简单模型的研究似乎在智力上具有挑战性，在技术上涉及到，部分原因是它需要理解远离平衡的系统属性。第二个项目致力于研究由介观标准金属桥连接的超导引线组成的结的非平衡性质。在这样的SNS节点中，即使在最小的应用偏差的极限下，也不可避免地会出现偏离平衡的情况；发展一个充分的理论对许多应用都很重要。同时，这也提出了一个严峻的挑战，因为目前还没有方便的理论工具来预测SNS结构的强非平衡态的行为。第三个项目旨在获得耦合到量子化辐射场的超导量子比特的退相干率的估计。我们将集中讨论与形成量子比特的超导颗粒中的准粒子激发有关的机制。该研究与实验相关，可能会解决一些现有的难题。进步将有助于进一步发展几种分析技术。研究生将得到培训。研究结果将影响介观超导、冷原子气体和量子混沌等多个领域。本理论研究探讨了与超导结的非平衡特性及其与混沌的关系，涉及超导体的结构及其在量子计算机中的潜在应用有关的许多主题。学生将接受培训，并为实验建立联系

This grant supports theoretical research in fundamental condensed matter physics. In the past decade a strong experimental effort was devoted to mesoscopic superconductivity. Currently, the interest in this field has increased even more because of the search for viable schemes in quantum computing. The parallel work in theory until recently was concentrated mostly on equilibrium characteristics and linear response properties of superconducting and hybrid structures. However, there is a clear need, dictated by experiments, to understand the properties of hybrid structures far from equilibrium. This research will explore these properties.The first project deals with dynamic properties of circuits of small Josephson junctions subject to parametric excitation. The driven junctions system may be brought to the regime of classical or quantum dynamic chaos. Quantum effects become important if the junctions are small enough to allow for charge quantization. We will explore the chaos in a system of two junctions. It appears that investigation of such a simple model may be intellectually challenging and technically involved, in part because it requires understanding of the system properties far from equilibrium.The second project is devoted to the study of non-equilibrium properties of a junction consisting of superconducting leads connected by a mesoscopic normal metal bridge. In such SNS junctions, deviations from equilibrium arise inevitably, even in the limit of the smallest applied biases; developing an adequate theory is important for many applications. At the same time, it presents a serious challenge , as currently there are no convenient theoretical tools for predicting the behavior of strongly non-equilibrium states of SNS structures.The third project aims at obtaining estimates of the decoherence rate for a superconducting qubit coupled to a quantized radiation field. We will concentrate on mechanisms associated with the quasiparticle excitations in the superconducting grains forming the qubit.The research is relevant to experiment and may resolve several existing puzzles. Advances will aid further development of several analytical techniques. Graduate students will be trained. Results of the research will affect a number of fields including mesoscopic superconductivity, cold atomic gases and quantum chaos.%%%This theoretical research explores a number of topics related to non-equilibrium properties of superconducting junctions and their relation to chaos, structures of involving superconductors and their potential use in quantum computers. Students will be trained and connections made to experiment.***