Department of Physics, Harvard University, Cambridge, MA, USA.
Institute for Quantum Information and Matter, California Institute of Technology, Pasadena, CA, USA.
Nature. 2019 May;569(7754):93-98. doi: 10.1038/s41586-019-1148-9. Epub 2019 Apr 24.
Topological superconductors can support localized Majorana states at their boundaries. These quasi-particle excitations obey non-Abelian statistics that can be used to encode and manipulate quantum information in a topologically protected manner. Although signatures of Majorana bound states have been observed in one-dimensional systems, there is an ongoing effort to find alternative platforms that do not require fine-tuning of parameters and can be easily scaled to large numbers of states. Here we present an experimental approach towards a two-dimensional architecture of Majorana bound states. Using a Josephson junction made of a HgTe quantum well coupled to thin-film aluminium, we are able to tune the transition between a trivial and a topological superconducting state by controlling the phase difference across the junction and applying an in-plane magnetic field. We determine the topological state of the resulting superconductor by measuring the tunnelling conductance at the edge of the junction. At low magnetic fields, we observe a minimum in the tunnelling spectra near zero bias, consistent with a trivial superconductor. However, as the magnetic field increases, the tunnelling conductance develops a zero-bias peak, which persists over a range of phase differences that expands systematically with increasing magnetic field. Our observations are consistent with theoretical predictions for this system and with full quantum mechanical numerical simulations performed on model systems with similar dimensions and parameters. Our work establishes this system as a promising platform for realizing topological superconductivity and for creating and manipulating Majorana modes and probing topological superconducting phases in two-dimensional systems.
拓扑超导体可以在其边界处支持局域的马约拉纳态。这些准粒子激发遵循非阿贝尔统计，可用于以拓扑保护的方式对量子信息进行编码和操作。尽管在一维系统中已经观察到马约拉纳束缚态的特征，但人们仍在努力寻找不需要微调参数且易于扩展到大量状态的替代平台。在这里，我们提出了一种实现马约拉纳束缚态二维结构的实验方法。我们使用由 HgTe 量子阱与薄膜铝制成的约瑟夫森结，通过控制结两端的相位差并施加面内磁场，能够调谐从平庸超导态到拓扑超导态的转变。我们通过测量结边缘的隧道电导来确定所得超导体的拓扑状态。在低磁场下，我们在零偏压附近的隧道谱中观察到一个最小值，这与平庸超导一致。然而，随着磁场的增加，隧道电导在零偏压处出现一个峰值，这个峰值在相位差的一个范围内持续存在，且这个范围随着磁场的增加而系统地扩展。我们的观察结果与该系统的理论预测以及对具有相似尺寸和参数的模型系统进行的全量子力学数值模拟一致。我们的工作确立了这个系统作为实现拓扑超导、创建和操纵马约拉纳模式以及探测二维系统中拓扑超导相的有前途的平台。
