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      Topological Andreev bands in multiterminal Josephson junctions

      報告題目   Topological Andreev bands in multiterminal Josephson junctions
      報告人   Dr. Hong-Yi Xie
      報告人單位   Beijing Academy of Quantum Information Sciences
      報告時間   2021-10-14 16:00:00
      報告地點   合肥微尺度物質科學國家研究中心物質科研B樓B0902會議室
      主辦單位   合肥微尺度物質科學國家研究中心、國際功能材料量子設計中心(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.