Measurements of Current-Phase Relationships in Josephson Junctions

非技术摘要：量子器件在计算、通信和传感方面具有非凡的前景。为了实现这一潜力，科学家和工程师必须找到正确的物理系统，在其中实现量子比特，称为量子位，错误率足够低。小型超导器件是构建量子比特功能物理器件最有希望的候选者之一。这项研究旨在解决有关小型超导器件性质的基本问题。研究人员通过灵敏的磁测量来检测流经超导器件的电流，以确定它是具有传统超导状态还是非常规的“拓扑”超导状态。拓扑超导态是在其边界处拥有特殊模式的态，称为马约拉纳模式。与其他类型的量子比特相比，基于这些马约拉纳模式的量子比特可以大大减少错误。技术摘要：提出的拓扑量子比特的操作是基于一种特殊的零能量模式，即马约拉纳模式。本研究的目的是利用新一代快速、高灵敏度的超导量子干涉器件（SQUID）传感器，通过实验证明马约拉纳模式的存在。两个最重要的性质是电流相关系，这是一个基本的关系，如果马约拉纳状态存在并且稳定，它就会有马约拉纳状态的决定性签名，以及宇称寿命，它决定了马约拉纳状态稳定的时间。该实验解决了传统（非拓扑）介观超导中长期存在的问题，例如具有完美传输的可调谐少模结的行为。它们还解决了拓扑器件中更新、更紧迫的问题，比如马约拉纳费米子存在于哪个系统中，以及它们的性质稳定多久。马约拉纳的实现和控制，作为具有非阿贝尔统计量的工程粒子的实验实例，具有重要的基础意义，也可以实现某些量子信息技术。这些活动还促进了快速、超灵敏、相对无创的磁测量技术的发展。研究人员积极参与社区和外展活动，旨在为各级理科生提供榜样和体验式学习。参与这项研究的学生和博士后研究人员在纳米技术、低温学、量子科学和精密测量方面受过良好的训练，并为作为教育工作者和科学家的一生做出贡献做好了准备。

Non-technical abstract: Quantum devices have exceptional promise for computation, communication, and sensing. To realize this potential, scientists and engineers must find the right physical system in which to implement quantum bits, called qubits, with sufficiently low error rates. Small superconducting devices are one of the most promising candidates for building physical devices that function as qubits. This research seeks to address fundamental questions about the nature of small superconducting devices. The researchers make sensitive magnetic measurements to detect the current flowing through a superconducting device to determine whether it has a conventional superconducting state or an unconventional, "topological" superconducting state. Topological superconducting state are states that host special modes at their boundaries, called Majoranas modes. Qubits based on these Majorana modes could greatly reduce errors compared to other types of qubits. Technical abstract:The proposed operation of topological qubits is based on a special zero-energy modes known as Majorana modes. The objective of this research is to experimentally demonstrate the existence of Majorana modes using a new generation of fast, highly sensitive Superconducting Quantum Interference Device (SQUID) sensors. The two most important properties are the current-phase relation, a fundamental relation that will have conclusive signatures of Majoranas if they are present and stable, and the parity lifetime, which determines how long the Majorana states are stable. The experiments address longstanding questions in conventional (non-topological) mesoscopic superconductivity, such as the behavior of tunable few-mode junctions with perfect transmission. They also address newer, more urgent questions in topological devices, such as in which systems Majorana fermions exist and for how long their properties are stable. The realization and control of Majoranas would have great foundational significance as an experimental instance of engineered particles with non-Abelian statistics and could also enable certain quantum information technologies. The activities additionally foster the development of fast, ultrasensitive magnetic measurement techniques that are relatively noninvasive. The researchers engage actively in community and outreach activities designed to provide role models and experiential learning to science students at all levels. Student and postdoctoral researchers involved in the research are well-trained in nanotechnology, cryogenics, quantum science, and precision measurements, and are prepared for a lifetime of contributions both as educators and as scientists.