题 目： Majorana Fermion as Quasiparticle Excitation in Topological Superconductors

报告人：Professor Xiao HU

          International Center for Materials Nanoarchitectonics (WPI-MANA)

         National Institute for Materials Science, Tsukuba 305-0044, Japan

时 间：2012年8月7日(星期二)10:00

地 点：中心教学楼701

Abstract：
Majorana fermions in topological superconductor are attracting significant interest, since topological quantum computation can be achieved based on the non-Abelian statistics of MF braiding, which is noise tolerant and decoherence free due to the topological protection of MF state. A realistic protocol for the MF braiding is one of the topmost issues to be addressed. We design a quantum device in which MFs associated with vortices in topological superconductor are generated, fused, transported, and braided easily by applying adiabatically gate voltages at point-like constriction junctions. Solving the time-dependent Bogoliubov-de Gennes equation, we demonstrate that MF braiding obeys the non-Abelian statistics. Our scheme is superior to other proposals because, first, no fine tuning on the value of gate voltage is necessary, and secondly gate voltages are applied at point-like positions which reduces perturbation to the MF state to negligible level.
I will also introduce novel Josephson phenomena with MFs involved. We show that a SQUID with one MF Josephson junction and a conventional SIS Josephson junction exhibits different critical currents for two current directions. This induces a ratchet potential for phase particle is an RCSJ system, and results in a voltage rectification when an ac current is injected.
This work is a collaboration with Q. –F. Liang, Z. Wang and L. –H. Wu. It has been supported by WPI Initiative on Materials Nanoarchitectonics, MEXT, Japan.
Curriculum Vitae:
Name: Xiao HU 
Position:   Principal Investigator and Unit Director
Institution:  International Center for Materials Nanoarchitectonics (WPI-MANA),
National Institute for Materials Science, Japan
Address: Namiki 1-1, Tsukuba 305-0044, Japan
http://www.nims.go.jp/mana/lab/theorphys/index.html
Research Experience and Position
April 1990:   Postdoctoral researcher in Physics Department, University of Tokyo
March 1991:  Research associate in Institute for Materials Research, Tohoku University
April 1995:   Visiting scientist at National Institute of Standards and Technology, USA
March 1996:  Associate professor in Institute for Materials Research, Tohoku University
May 1996:   Senior researcher in National Research Institute for Metals (NRIM), Science and Technology Agency, Japan
April 1999:   Group leader, NRIM
April 2002:   Group Director, National Institute of Materials Science (NIMS)
October 2007: Principal Investigator, World Premium International Center for Materials Nanoarchitectonics (MANA), NIMS

Research fields
[1] exotic magnetism and nano magnetism
[2] novel superconductivity and vortex states
[3] Majorana fermion in topological systems

Selected Papers
[1] Massless Leggett Mode in Multi-band Superconductors with Time-Reversal-Symmetry Breaking, Lin SZ and Hu X, Phys Rev Lett, 2012; 108: 177005
[2] A Prospective Material for Spintronics: Half-Metallic Antiferromagnet, Hu X, Adv Mater, 2012; 24: 294 (review article)
[3] Interference and Switching of Josephson Current Carried by Nonlocal Spin-Entangled Electrons in a SQUID-like System with Quantum Dots, Wang Z and Hu X, Phys Rev Lett, 2011; 106: 037002
[4] Phase dynamics in a stack of inductively coupled intrinsic Josephson junctions and terahertz electromagnetic radiation, Hu X and Lin SZ, Supercond Sci Technol, 2010; 23: 253001 (review article)
[5] Possible dynamic states in inductively coupled intrinsic Josephson junctions of layered high-Tc superconductors, Lin SZ and Hu X, Phys Rev Lett, 2008; 100: 247006.
[6] Possible half metallic antiferromagnet in a hole-doped perovskite cuprate predicted by first-principles calculations, Nie YM, Hu X, Phys Rev Lett, 2008; 100: 117203.
[7] Depinning and creep motion in glass states of flux lines, Luo MB and Hu X, Phys Rev Lett, 2007; 98: 267002.
[8] Orbital order and ferrimagnetic properties of the new compound Sr8CaRe3Cu4O24, Wan XG, Kohno M and Hu X, Phys Rev Lett, 2005; 94: 087205.
[9] Possible spin triplet superconductivity in NaxCoO2/•yH2O, Tanaka A and Hu X, Phys Rev Lett, 2003; 91: 257006.
[10] Effects of point defects on the phase diagram of vortex states in high-Tc superconductors in the B || c axis, Nonomura Y and Hu X, Phys Rev Lett, 2001; 86: 5140.
[11] δ-function peak in the specific heat of high-Tc superconductors: Monte Carlo simulation, Hu X, Miyashita S and Tachiki M, Phys Rev Lett, 1997; 79: 3498

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