Reproducing topological properties with quasi-Majorana states
Reproducing topological properties with quasi-Majorana states
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DOI：
10.21468/scipostphys.7.5.061
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发表时间：
2018-06
期刊：
影响因子：
5.5
通讯作者：
A. Vuik;B. Nijholt;A. Akhmerov;M. Wimmer
中科院分区：
文献类型：
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作者：
A. Vuik;B. Nijholt;A. Akhmerov;M. Wimmer
只要限制势足够平滑，混合超导-半导体器件中的安德烈夫束缚态在拓扑平凡状态下就可以具有接近于零的能量。这些准马约拉纳态在拓扑平凡相中表现出零偏置电导特征，模仿空间分离的拓扑马约拉纳态。我们表明，除了准马约拉纳态之间的耦合受到抑制之外，这些态穿过隧道势垒到外部的耦合也随着磁场的增加而呈指数变化。因此，准马约拉纳态模仿了大多数提出的马约拉纳特征：量化的零偏置峰值、4\pi4π 约瑟夫森效应以及存在正常量子点时的隧道谱。我们将开放状态中的量子化电导下降而不是峰值确定为真正的马约拉纳态除了具有体拓扑转变之外的显着特征。由于编织方案仅依赖于耦合到各个马约拉纳态的能力，因此对耦合强度的指数控制还允许使用准马约拉纳态进行编织。因此，虽然准马约拉纳态的出现使拓扑马约拉纳态的观察变得复杂，但它为非阿贝尔任意子编织和受保护的量子计算开辟了一条替代途径。
Andreev bound states in hybrid superconductor-semiconductor devices can have near-zero energy in the topologically trivial regime as long as the confinement potential is sufficiently smooth. These quasi-Majorana states show zero-bias conductance features in a topologically trivial phase, mimicking spatially separated topological Majorana states. We show that in addition to the suppressed coupling between the quasi-Majorana states, also the coupling of these states across a tunnel barrier to the outside is exponentially different for increasing magnetic field. As a consequence, quasi-Majorana states mimic most of the proposed Majorana signatures: quantized zero-bias peaks, the 4\pi4π Josephson effect, and the tunneling spectrum in presence of a normal quantum dot. We identify a quantized conductance dip instead of a peak in the open regime as a distinguishing feature of true Majorana states in addition to having a bulk topological transition. Because braiding schemes rely only on the ability to couple to individual Majorana states, the exponential control over coupling strengths allows to also use quasi-Majorana states for braiding. Therefore, while the appearance of quasi-Majorana states complicates the observation of topological Majorana states, it opens an alternative route towards braiding of non-Abelian anyons and protected quantum computation.