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Quantentechnologie

Dieter Meschedes Forschungsgruppe
Home AMO-Physikkolloquien
Colloquia
  • David DiVincenzo

    (27/10/15)
  • Invited speaker: Prof. David DiVincenzo
    Affiliation: RWTH Aachen, FZ Jülich
    Title: Engineering the Quantum Computer: A Case Study of the Circulator

    Time and room:  17:15 h, lecture hall IAP
    Abstract: The Faraday-effect circulator was invented in the 1950's, based on some fundamental theoretical insights about the role of nonreciprocity in transmission systems. These Faraday devices are used successfully at both optical and at microwave frequencies; the latter have a unique and essential role in making solid-state quantum computing work. Also in the 1950's, microwave circulators based on a very different phenomenon, the Hall effect, were also considered. It was "proved" then that a Hall bar cannot make a good gyrator (a close cousin to the circulator). This proof is flawed, and we have shown that good gyrators are possible for Hall angle -> 90 degrees (aka "quantum Hall") if the device is contacted capacitively. We predict that the resulting Hall circulator can be much more miniaturized than the Faraday kind, and I will show some preliminary experimental efforts in this direction. I will discuss the relation of this device functionality to the physics of chiral edge magnetoplasmons in the Hall conductor.
     

  • Thilo Kopp

    (30/06/15)
  • Invited speaker: Prof. Thilo Kopp
    Affiliation: Universität Augsburg
    Title: Superconductivity With Rashba Spin-Orbit Coupling And Magnetic Field:
    A Route To Topological Superconductivity

    Time and room:  17:15 h, lecture hall IAP
    Abstract: A two-dimensional s-wave superconductor in a magnetic field with a sufficiently strong Rashba spin-orbit coupling is a candidate system for a topological superconductor. Typically, the required magnetic field to convert the superconductor into a topologically non-trivial state is however by far larger than the upper critical field, which excludes its realization. This problem is overcome by rotating the magnetic field into the superconducting plane. The character of the superconducting state changes with the strength and the orientation of the magnetic field. A topological state indeed extends to an in-plane field orientation. Mapping the spin texture in momentum space reveals a meron-like structure. In analogy to skyrmion patterns, the momentum-space spin texture translates into an integer number which offers an alternative to reflect the topological character of the superconducting state. A possible realization of the topological s-wave superconductor at LaAlO3/SrTiO3 interfaces is examined.

  • Nathan Goldman

    (23/06/15)
  • Invited speaker: Prof. Nathan Goldman
    Affiliation: Université Libre de Bruxelles
    Title: Measuring Chern Numbers with Cold Atoms: From 2D to 4D Quantum Hall Physics

    Time and room:  17:15 h, lecture hall IAP
    Abstract: In this talk, I will describe how Bloch bands with non-trivial topology can be engineered and probed in cold-atom systems. I will first briefly describe a scheme by which the topological Chern number has been extracted from a Bose gas trapped in a 2D modulated optical lattice [1]. I will then explain how this scheme can be extended to access 4D quantum Hall physics using the concept of synthetic dimensions [2]. In particular, I will present a proposal for measuring the second Chern number, an emblematic topological invariant associated with 4D Bloch bands [3].

    [1] Measuring the Chern number of Hofstadter bands with ultracold bosonic atoms, M. Aidelsburger, M. Lohse, C. Schweizer, M. Atala, J. T. Barreiro, S. Nascimbène, N. R. Cooper, I. Bloch, N. Goldman, Nature Physics 11, 162–166 (2015)
    [2] Synthetic gauge fields in synthetic dimensions, A. Celi, P. Massignan, J. Ruseckas, N. Goldman,
    I. B. Spielman, G. Juzeliunas, and M. Lewenstein, Phys. Rev. Lett. 112, 043001 (2014)
    [3] Four_Dimensional Quantum Hall Effect with Ultracold Atoms, H. M. Price, O. Zilberberg, T. Ozawa, I. Carusotto, N. Goldman, arXiv:1505.04387

  • Fabian Heidrich-Meisner

    (16/06/15)
  • Invited speaker: Dr. Fabian Heidrich-Meisner
    Affiliation: LMU München
    Title: Relaxation Dynamics and Transport in the One-Dimensional Fermi-Hubbard Model

    Time and room:  17:15 h, lecture hall IAP
    Abstract: The Hubbard model harbors the key ingredients to obtain Mott-insulating behavior and antiferromagnetism and is thus a paradigmatic model for the description of strongly correlated electron systems. Besides its relevance for condensed matter systems, several experiments with ultra-cold quantum gases have realized this system using optical lattices. A major interest is in the non-equilibrium dynamics of strongly interacting closed many-body systems, aiming at an understanding of thermalization and relaxation dynamics. I will describe the relaxation dynamics in this model in the quantum quench starting from a perfect Neel state. Since a spontaneous breaking of a continuous symmetry is prohibited in one dimension, the order parameter decays to zero. Our numerical analysis unveils the characteristic time scales for the dynamics of spin- and charge-excitations and their fingerprints in the time evolution of observables. In a second part, I will turn to the discussion of transport properties. Integrable one-dimensional quantum systems are known to be prone to possess anomalous conductivities.
    We compute the thermal conductivity, show that it diverges, and discuss implications for experiments with real materials and ultracold atoms in optical lattices.
     

  • Enrique Solano

    (12/06/15)
  • Special Colloquium

    Invited speaker: Prof. Enrique Solano
    Affiliation: University of the Basque Country, Bilbao
    Title: Quantum Simulation of the Quantum Rabi Model

    Time and room: 15:15 h, lecture hall Helmholtz-Institut für Strahlen- und Kernphysik
    Abstract: