EAGER: Braiding of Majorana Zero Modes in the Quantum Hall - Superconductor Hybrids

非技术摘要：半导体电子学目前依赖于电子和空穴的流动，但其他类型的粒子状“激发”可以人工创造和控制。这些激发包括所谓的Majorana费米子和非阿贝尔任意子，它们具有保护它们免受外部扰动的性质。由于这种健壮性，对这种“拓扑激发”的控制将使电子学发生革命性变化，并使量子计算更接近现实。在过去的几年里，凝聚态研究界在拓扑激发的实际实现方面取得了巨大的进展。人们确实意识到，它们可以通过在某些类型的低维材料(如半导体纳米线)中诱导超导电性来人工创造。PI提出了一种替代方法来产生基于石墨烯的拓扑激发，该石墨烯受到强磁场并耦合到超导电极上。单独的拓扑激发通过可选的链接连接在一起，允许一个人可控地耦合和操纵它们。主体材料的平面性质应该有助于制造这些设备的多个副本，从而能够实现未来的缩放和与传统电子设备的集成。该项目非常强调指导和教育：它涉及两名博士生，以及一名本科生和一名高中生。将招募NC科学与数学学校的高中生参加实验室活动，感受物理研究。这项研究将对研究生和本科生进行与工业和学术生涯相关的测量和纳米制造方法的培训。技术摘要：主要研究小组去年报告了在量子霍尔效应范围内首次观测到通过二维区域的超导电流，该结基于第二类超导体接触的石墨烯。这一结果证明了超导电极与量子霍尔边态相干耦合的能力。它允许首席研究小组以更复杂的几何结构接近超导体-量子霍尔界面，预计这些界面将容纳Majorana费米子。具体的目标是在量子霍尔台面上蚀刻出准一维“沟槽”形状的超导电极，边缘状态在接触的相反一侧反向传播。已经预测，在自旋极化的量子霍尔区(例如，填充因子等于1时)，在沟槽的末端形成Majorana零模。要实现这些器件，需要对量子霍尔态和超导体之间的耦合有基本的了解，以及开发制造技术来在超导接触和量子霍尔主体材料之间设计非常干净的界面。在这方面，石墨烯可以提供很多东西：可调的能带结构和卓越的电子质量，这导致在相对较低的磁场下出现自旋极化的量子霍尔态。一旦形成，Majoranas零模可以通过可选通的边缘状态链路连接起来，允许人们可控地融合(混合)它们。可以在同一个台面上制作这些激发的多个副本，从而实现它们的编织。主体材料的平面性质应便于制造这些器件的多个副本，从而实现未来的缩放和与传统读出电子设备的集成。最后但同样重要的是，这些测量有望揭示非阿贝尔任意子的迷人物理学，这些任意子具有与任何传统准粒子截然不同的性质。这些拓扑激发与一整类混合拓扑设备相关，并可能导致有助于使量子计算成为现实的突破。

Non-technical Abstract:Semiconductor electronics currently relies on the flow of electrons and holes, but other types of particle-like "excitations" can be artificially created and controlled. These excitations, which include so-called Majorana fermions and non-abelian anyons, have properties that protect them against external perturbations. As a result of this robustness, control over such "topological excitations" would revolutionize electronics and bring quantum computing closer to reality. Over the past few years, the condensed matter research community achieved dramatic progress in the practical implementation of topological excitations. It was indeed realized that they could be artificially created by inducing superconductivity into certain types of low-dimensional materials such as semiconducting nanowires. The PI proposes an alternative approach to create the topological excitations based graphene subject to high magnetic fields and coupled to superconducting electrodes. The individual topological excitations are connected by gateable links, allowing one to controllably couple and manipulate them. The planar nature of the host material should facilitate making multiple copies of these devices, enabling future scaling and integration with conventional electronics. The project strongly emphasizes mentoring and education: it involves two PhD students, and undergraduate and a high school student. High school students from the NC School of Science and Math will be recruited to participate in the laboratory activities and get a feel for physics research. This research will train the graduate and undergraduate students in the measurement and nanofabrication methods relevant for both industrial and academic careers.Technical Abstract:Working with Josephson junctions based on graphene contacted by type II superconductor, the principal investigator's group reported last year on the first observation of supercurrent through a two-dimensional region in the regime of the quantum Hall effect. This result proves the capability to coherently couple the superconductor electrodes to the quantum Hall edge states. It allows the principal investigator's group to approach superconductor-quantum Hall interfaces with more complex geometries, which are expected to host Majorana fermions. The specific goals are the superconducting electrodes in a shape of quasi-1D "trenches" etched in a quantum Hall mesa, with the edge states counter-propagating on the opposite sides of the contact. It has been predicted that in the spin-polarized quantum Hall regime (for example, at the filling factor equal to one), Majorana zero modes are formed at the ends of the trenches. Realizing these devices requires fundamental understanding of the coupling between the quantum Hall states and superconductor, as well as the development of fabrication techniques to design extremely clean interfaces between the superconducting contacts and the quantum Hall host material. Graphene has much to offer in that regard: a tunable band-structure and a remarkable electronic quality, which results in the appearance of the spin-polarized quantum Hall states at relatively low magnetic fields. Once formed, the Majoranas zero modes could be connected by gateable edge-state links, allowing one to controllably fuse (hybridize) them. Multiple copies of these excitations could be fabricated on the same mesa, enabling their braiding. The planar nature of the host material should facilitate making multiple copies of these devices, enabling future scaling and integration with conventional read-out electronics. Last but not least, the measurements are expected to reveal the fascinating physics of non-abelian anyons, which have properties distinctly different from any conventional quasiparticles. These topological excitations are relevant to a whole class of hybrid topological devices and could lead to breakthroughs that help make quantum computing a reality.