报告题目：Seminar Series on Topological Quantum Information Technology

报告时间：2016年7月29日14：00-17：00

报告地点：物理系三楼报告厅（理科楼C302）

报 告 1：Majorana Fermions in Ballistic Nanowire Devices

报 告 人：Hao Zhang (张浩)，QuTech, Applied Science, TU Delft

报告摘要：Since the first experiment on Majoranas in 2012[1], the observed zero-bias-peak as a signature of Majorana fermions has been hotly debated with a zoo of arguments and alternative explanations. Most of them are based on disorders, which can mimic Majorana signatures in the system. Here[2], we show that, with significantly improvement of device fabrication, we clean up this debate by ruling out disorders in our system. By applying a magnetic field, a stable zero-bias-peak in this ballistic enviroment helps us to falsify all other alternatives. The only theory still standing is the Majorana theory. The zero-bias-peak exists in a stable gate voltage and magnetic field range, which is consistent with the Majorana topological phase diagram.

[1] Mourik et al., Science 2012

[2] Zhang et al., arxiv: 1603.04069.

报 告 2：Majorana zero modes and diabatic errors in Majorana qubit

报 告 人：Dong Liu (刘东)，Microsoft Research Station Q

报告摘要：Topological materials provide a protection from decoherence at the hardware level by using emergent non-Abelian anyons. The simplest non-Abelian anyon involves a defect that binds a Majorana zero-energy mode, predicted to appear quite naturally in certain superconducting systems. Direct tunneling spectroscopy method provides the simplest way to measure the presence of the zero-energy state at the defect. However, the zero-bias peak in tunneling conductance might originate from the other mechanisms giving false-positive signatures. In this talk, I will introduce two simple measurement schemes to overcome the problem, and show robust, clear, and universal experimental signatures of MZMs.

Majorana zero modes provide a potential platform for the storage and processing of quantum information with intrinsic error rates that decrease exponentially with inverse temperature and with the length scales of the system. However, it is less well-understood how error rates depend on the speed with which non-Abelian quasiparticles are braided. In general, diabatic corrections only vanish as a power-law function with the length of time for the braid. This power-law behavior can wash out the advantages of topological quantum computation. In this talk, I will show that such diabatic errors can be detected and corrected by applying a sequence of parity measurements.