EAGER: BRAIDING: Majorana modes in monolayer topological insulator WTe2

非技术摘要：寻找量子计算的替代途径是目前最重要的，目前的方法面临许多障碍。最大的问题是量子比特的退相干，这意味着量子信息量随着时间呈指数衰减。从原理上讲，可以通过“拓扑保护”来避免退相干。已知的唯一现实的拓扑保护方案是基于所谓的Majorana模创建量子比特，Majorana模是出现在某些类型的量子线末端的特殊状态。制作Majoranas的一种方法是使用存在于拓扑绝缘体边缘的特殊量子线。实验学家PI最近发现了第一个天然的单层二维(2D)拓扑绝缘体，这表明在2D材料中创造和操纵Majoranas是可能的。合作者是拓扑现象方面的理论家和专家；在这个项目中，他们合作寻找在这个系统中创建和检测Majoranas的最简单方法。这项工作支持研究生从事跨学科的专题工作，理论和实验齐头并进，这可能会催生下一次信息革命。该项目在华盛顿大学和当地业界(包括微软)之间建立了一座桥梁，后者在2D材料方面的研究工作处于领先地位，而当地业界(包括微软)正在大力投资于量子计算机的应用。技术：该项目旨在建立2D材料平台的可行性，以创建可用于拓扑量子处理的Majorana零模。该团队使用单层WTe2作为2D拓扑绝缘体，结合2D超导体(NbSe2或FeSe)和2D磁体(CrI3或CrBr3)。这些材料与电接触和隧道势垒一起堆积成范德瓦尔斯异质结构。在这三种物质相遇的地方，在低温下可能会出现马约拉纳模式，可以通过隧道测量来探测。与其他Majorana系统相比，这种2D平台提供了优势，包括不需要磁场来产生螺旋模式，并且可以避免精细的化学势调节。涉及的多电子和拓扑物理的复杂性，以及系统的新颖性，要求实验和理论之间的密切合作。具体目标是诱导和了解WTe2螺旋边缘的超导邻近间隙，并设计和测试可能出现和检测到Majoranas的最简单的2D异质结构设备。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Nontechnical Abstract: Finding alternative paths to quantum computing is paramount at this time, and current approaches face many hurdles. The biggest is decoherence of the qubits, meaning that the quantum information content decays exponentially with time. In principle, decoherence can be avoided using "topological protection". The only realistic known scheme for topological protection is based on creating the qubits from so-called Majorana modes, which are peculiar states that occur at the ends of certain types of quantum wires. One way to make Majoranas is using the special quantum wire that exists at the edge of a topological insulator. The PI, an experimentalist, recently discovered the first natural monolayer two-dimensional (2D) topological insulator, suggesting the possibility to create and manipulate Majoranas in 2D materials. The co-PI is a theorist and expert on topological phenomena; in this project they collaborate to find the simplest way to create and detect Majoranas in this system. The work supports graduate students in topical interdisciplinary work where theory and experiment go hand in hand, and which could conceivably give birth to the next information revolution. The project forms a bridge between the University of Washington, which has a leading research effort in 2D materials, and local industry (including Microsoft) which is investing heavily in applications of quantum computers.Technical: This project aims to establish the viability of the 2D materials platform for creating Majorana zero modes that could be used for topological quantum processing. The team employs monolayer WTe2 as a 2D topological insulator, combined with a 2D superconductor (NbSe2 or FeSe) and a 2D magnet (CrI3 or CrBr3). These materials are stacked into a van der Waals heterostructure along with electrical contacts and tunnel barriers. At the point where the three materials meet a Majorana mode may appear at low temperatures and can be probed by tunneling measurements. This 2D platform offers advantages compared with other Majorana systems including that no magnetic field is required to produce the helical mode, and the possibility to avoid delicate tuning of the chemical potential. The complexity of the many-electron and topological physics involved, and the novelty of the system, calls for close cooperation between experiment and theory. Specific goals are to induce and understand a superconducting proximity gap in the helical edge of WTe2, and to design and test the simplest 2D possible heterostructure devices in which Majoranas may occur and be detected.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.