Topological Graphene Multiterminal Josephson Junctions

量子系统的拓扑性质近年来引起了理论和实验的广泛关注。非平凡的拓扑性质通常来自内在的材料性质，例如， 具有强自旋轨道相互作用的材料中的拓扑能带结构。另一种可能性是混合结构中不同材料的组合以产生拓扑能带结构。这些实现需要复杂的材料，这往往是很难synthesized.Recently，它已被预测，由传统材料制成的多端约瑟夫森结主机拓扑非平凡状态的人工能带结构控制的宏观相的超导终端。这些系统提供了可能性，调整拓扑性质原位的外部参数，因此允许相当大的灵活性的调查topology.The项目的目的是一个联合的实验和理论的努力，实现和理解人工拓扑能带结构的多端约瑟夫森结。我们项目选择的材料是石墨烯。由于其二维性质，石墨烯提供了充分的设计灵活性，而其固有的高质量和栅极可调性允许控制弹道传输到单个量子通道。因此，石墨烯是研究拓扑多端约瑟夫森结的主要候选材料。我们计划通过量子化非局域电导和微波光谱在一个最小的系统，一个四端约瑟夫森结明确识别和表征拓扑Andreev状态。一个长期目标是使用石墨烯多端结来模拟更高有效维度的拓扑结构。

Topological properties of quantum systems have recently attracted considerable theoretical and experimental attention. Nontrivial topological properties usually follow from intrinsic material properties, e.g., topological band structures in materials with strong spin-orbit interaction. Another possibility is the combination of different materials in hybrid structures to create topological band structures. These implementations require complex materials which are often difficult to synthesize.Recently, it has been predicted that multiterminal Josephson junctions made of conventional materials host topologically nontrivial states in an artificial band structure controlled by the macroscopic phases of the superconducting terminals. These systems offer the possibility to tune topological properties in situ by external parameters, and therefore allow considerable flexibility for the investigation of topology.The aim of this project is a joint experimental and theoretical effort to implement and understand artificial topological band structures in multiterminal Josephson junctions. The material of choice for our project is graphene. Due to its two-dimensional nature, graphene offers full flexibility of design, while its intrinsic high quality and gate tunability allows control of ballistic transport down to single quantum channels. Therefore, graphene is a prime candidate for the investigation of topological multiterminal Josephson junctions. We plan to unambiguously identify and characterize topological Andreev states via quantized nonlocal conductance and microwave spectroscopy in a minimal system, a four-terminal Josephson junction. A long-term goal is to use graphene multiterminal junctions to simulate topology in higher effective dimensions.