Probing topological effects in multiterminal Josephson junction devices

将材料分为固体、液体和气体等不同的类别有助于澄清我们对这些材料性质的理解，从而提高我们在技术相关产品中使用它们的能力。最近，凝聚态物理中材料的分类方式发生了重大变化：许多材料的性质现在可以根据它们的拓扑分类来理解。拓扑学是物体和材料的基本特性。两个看起来完全不同的对象可能属于相同的拓扑类：一个甜甜圈和一个咖啡杯可能看起来是完全不同的对象，但它们都有一个孔，因此在拓扑上是相似的。上个世纪的许多突破性科学发现，如量子霍尔效应，现在已经根据其组成材料的拓扑特性重新解释，并且在此过程中获得了新的见解。设计具有特定拓扑特性的材料和器件也具有潜在的技术优势：例如，基于拓扑量子比特的量子计算机可能特别能抵抗由于量子退相干而产生的错误。然而，合成具有特定拓扑性质的材料和器件已被证明是混乱和困难的。该项目探索了一种利用超导混合器件开发具有拓扑重要特征的器件的新方法，在这种器件中，超导体与金或石墨烯等材料接触。这种器件的性质模拟了真实晶体的性质，通过适当的设计，可以制造出拓扑上有趣的晶体的类似物，从而可以研究拓扑上不同的系统。这些装置本身是用复杂的纳米光刻技术制造的，并在绝对零度以上几毫米的温度下进行测量。本项目所使用的基础物理和实验技术适用于广泛的科学研究，确保参与本项目的学生在未来的学术或工业职业生涯中得到良好的训练。技术摘要：具有拓扑非平凡带结构的材料由于其在包括拓扑量子计算在内的许多领域的潜在应用，目前正受到广泛的研究。这个项目的重点是利用超导混合装置，或将超导体与金或石墨烯等普通材料接触的装置，创造出拓扑上非平凡晶体的类似物。在与两个超导体接触的普通金属中，准粒子的能级取决于超导体之间的相位差，就像晶体中电子的能级取决于晶体动量一样。有了两个以上的超导体，就可以制造出高维晶体的类似物。这项工作的目标是通过复杂的纳米光刻技术，在毫开尔文温度下使用电输运测量，在专门设计的设备中寻找非平凡拓扑的特征。除了进一步加深我们对拓扑系统的理解之外，在本项目中获得的关于超导邻近效应性质的知识和理解，特别是在弹道器件中，将提高对拓扑量子计算目标邻近效应器件中超导相关性的理解。所需的纳米光刻和低温实验技术与量子信息科学新兴领域所需的技术相似，确保参与项目的学生在量子劳动力所需的技能方面得到良好的培训。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Non-technical AbstractThe sorting of materials into different classes such as solids, liquids and gases helps to clarify our understanding of the properties of these materials and consequently enhances our ability to use them in technologically relevant products. Recently, there has been a major shift in the way materials in condensed matter physics are classified: the properties of many materials can now be understood in terms of their topological classification. Topology is a fundamental characteristic of objects and materials. Two seemingly disparate objects may belong to the same topological class: a donut and a coffee cup may seem to be entirely different objects, but both have a single hole, and hence are topologically similar. Many groundbreaking scientific discoveries of the past century such as the quantum Hall effect have now been reinterpreted in terms of the topological properties of their constituent materials, and in doing so, new insights have been gained. Designing materials and devices with specific topological properties also has potential technological advantages: for example, quantum computers based on topological qubits may be especially resistant to errors due to quantum decoherence. However, synthesizing materials and devices with specific topological properties has proved messy and difficult. This project explores a new way to develop devices with topologically important characteristics using superconducting hybrid devices, devices in which a superconductor is placed in contact with a material like gold or graphene. The properties of such devices mimic those of real crystals, and by appropriate design, analogs of topologically interesting crystals can potentially be fabricated, enabling the study of topologically distinct systems. The devices themselves are fabricated using sophisticated nanolithography techniques and measured at temperatures a few millidegrees above absolute zero. The underlying physics and experimental techniques used in this proposal are applicable to a wide range of scientific research, ensuring that the students engaged in this project will be well trained for future careers in either academia or industry. Technical abstractMaterials with topologically non-trivial band structure are being studied intensively at the moment due to their potential applications in a number of areas, including in topological quantum computation. The focus of this project is to create analogs of topologically non-trivial crystals using superconducting hybrid devices, or devices in which superconductors are placed in contact with a normal material such as gold or graphene. The energy levels of quasiparticles in a normal metal in contact with two superconductors depend on the phase difference between the superconductors in much the same way as the energy levels of electrons in a crystal depend on the crystal momentum. With more than two superconductors, analogs of higher dimensional crystals can be fabricated. The goal of this effort is to search for signatures of non-trivial topology in specifically designed devices using electrical transport measurements at millikelvin temperatures, with the devices being fabricated by sophisticated nanolithography techniques. In addition to furthering our understanding of topological systems, the knowledge and understanding gained in this project about the nature of the superconducting proximity effect, particularly in the ballistic devices, will improve the understanding of superconducting correlations in proximity effect devices targeted to topological quantum computing. The nanolithography and low temperature experimental techniques required are similar to the techniques needed in emerging fields in quantum information science, ensuring that students involved in the project are well trained in skills required for the quantum workforce.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.