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Topological Andreev bands in multiterminal Josephson junctions

报告题目   Topological Andreev bands in multiterminal Josephson junctions
报告人   Dr. Hong-Yi Xie
报告人单位   Beijing Academy of Quantum Information Sciences
报告时间   2021-10-14 16:00:00
报告地点   long8手机网页版物质科研B楼B0902会议室
主办单位   long8手机网页版、国际功能材料量子设计中心(ICQD)


  We study the Josephson effect in the multiterminal junction of topological superconductors. We use the symmetry-constrained scattering matrix approach to derive band dispersions of emergent subgap Andreev bound states in the parameter space of superconducting phase differences. We find distinct topologically protected band crossings that serve as monopoles of finite Berry curvature. Particularly, in a four-terminal junction the admixture of 2π and 4π periodic levels leads to the appearance of finite-energy Majorana-Weyl nodes. This topological regime in the junction can be characterized by a quantized nonlocal conductance that measures the Chern number of the corresponding bands. In six-terminal junctions, crossings of Andreev bands may support the non-Abelian SU(2) monopoles with a topological charge characterized by the second class Chern number. We propose that these topological defects can be detected via nonlinear response measurement of the current autocorrelations. In addition, multiterminal Josephson junction devices can be tested as a hardware platform for realizing holonomic quantum computation. In addition, we calculate current-phase relations, variance, and cross correlations of topological supercurrents in multiterminal contacts and discuss the universality of these transport characteristics. At the technical level these results are obtained by integrating over the group of a circular ensemble that describes the scattering matrix of the junction. 


  Dr. Hong-Yi Xie, Associate Researcher, Beijing Academy of Quantum Information Sciences, obtained PhD in theoretical condensed matter physics at the International School for Advanced Study in Trieste (Italy) in 2012. From 2012 to 2016, he did postdoctoral research at the Abdus Salam International Centre for Theoretical Physics (Italy) and the Rice University (USA). From 2016 to 2019, he was appointed as Assistant Scientist at the University of Wisconsin-Madison (USA) before joining the BAQIS. Dr. Xie is a theorist and presently focuses on the transport properties of quantum systems involving disorder, interaction, and nontrivial topology. His research is concerned with novel systems such as graphene, Weyl semimetals, topological insulators and superconductors, and hybrid structures such as Josephson junctions and cavity polaritons.