Hot Topics in Quantum Nanoscience: Charles L. Kane (Univ. of Pennsylvania): “The Time Reversal Invariant Fractional Josephson Effect”



10:00 - 12:30 hrs


TU Delft, Applied Sciences, Lorentzweg 1 (room G, F207)


Hot Topics in Quantum Nanoscience

Course Content: Speakers from all over the world will be asked to present pedagogical introductions to their field with an emphasis on basic concepts. Besides such an introductory lecture open for everybody, the participants of this course will have an additional discussion with the speaker discussing a recent paper and the holy grails of the field.

Exemplary topics are topological insulators, mesoscopic quantum gravity, string theory for condensed matter, measurement-based quantum computing, quantum-limited sensors, Majorana Fermions, fast-light with single photons, etc., etc. For an overview of the previous sessions, please click here.

Audience: The tutorial, as a one hour lecture, is open to everybody. A second hour will be reserved as a discussion hour for the registered class of PhD students and postdocs with the lecturer.

Registration: it is not possible anymore to register for this session anymore.

Preparation: PhD students who have registered for this hot topics course need to prepare for the session by reading the articles that are mentioned in the below.

Date: Friday 10 October 2014

Speaker: professor Charles L. Kane (University of Pennsylvania)

Topic: “The Time Reversal Invariant Fractional Josephson Effect”

Abstract: Topological Superconductivity is a topic of current interest because of its potential for providing a new method for storing and manipulating quantum information.  One of the most basic consequences of topological superconductivity is the fractional Josephson effect, which arises due to the coherent tunneling of single electrons between two superconductors, leading to an AC Josephson effect with half the usual Josephson frequency.  In this talk we will review the theoretical foundations for the fractional Josephson effect and discuss prospects for observing it. We will then describe recent work in which we have clarified the role of time reversal symmetry. Time reversal symmetric Josephson junctions are classified by two distinct Z_2 topological invariants. One of these characterizes a junction mediated by the edge states of a quantum spin Hall insulator. In that case, we showed that electron interactions stabilize a "Z_4 fractional Josephson effect" with one quarter the usual Josephson frequency. For strong interactions this Josephson effect is associated with the tunneling of charge e/2 quasiparticles. For weak tunneling, this theory describes a fourfold ground state degeneracy that is similar to that of coupled "fractional" Majorana modes, but is protected by time reversal symmetry. 

Host: Prof. dr. ir. Leo Kouwenhoven

Location:  Delft University of Technology, TNW (building 22), Lorentzweg 1, Delft.

Room: TN College room G (F207) 

Time: 10:00 - 11:00 hot topics seminar, 11:00 - 12:30 hot topics discussion

Required reading:

Hot Topics paper: Time-Reversal-Invariant Z4 Fractional Josephson Effect, Zhang and Kane, PRL 113, 036401 (2014)

Preparation paper: Josephson current and noise at a superconductor/quantum-spin-Hall-insulator/superconductor Junction, Fu and Kane, PRB 79, 161408 (2009)