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Dieter Meschedes Forschungsgruppe
Home AMO-Physikkolloquien
  • Christoph Stampfer

  • Invited speaker: Christoph Stampfer
    Affiliation: RWTH Aachen and Forschungszentrum Jülich
    Title: Quantum Point Contacts in Graphene
    Time and room: 17:15, lecture hall IAP
    Abstract: Quantum point contacts are cornerstones of mesoscopic physics and central building blocks for quantum electronics. Although the Fermi wavelength in high-quality bulk graphene can be tuned up to hundreds of nanometers, the observation of quantum confinement of Dirac electrons in nanostructured graphene systems has proven surprisingly challenging. Here I show ballistic transport and quantized conductance of size-confined Dirac fermions in lithographically-defined graphene constrictions. The fabricated graphene constrictions are encapsulated in hexagonal boron nitride sheets allowing for high carrier mobilities. The constrictions have widths ranging from around 200 to 800 nm. At high charge carrier densities, the observed conductance agrees excellently with the Landauer theory of ballistic transport without any adjustable parameter. Experimental data and simulations for the evolution of the conductance with magnetic field unambiguously confirm the identification of size quantization in the constriction. Close to the charge neutrality point, bias voltage spectroscopy reveals a renormalized Fermi velocity of ~1.5x106 m/s in our graphene constrictions. Moreover, at low carrier density transport measurements allow probing the density of localized states at edges, thus offering a unique handle on edge physics in graphene devices.

  • Martin Schulze

  • Invited speaker: Martin Schultze
    Affiliation: MPI für Quantenoptik, Garching
    Title: Attosecond Spectroscopy of Multi-Electron Dynamics in Atoms and Solids
    Time and room: 17:15, lecture hall IAP
    Abstract: Light-matter interaction starts with light-field driven electron dynamics. Attosecond spectroscopy can achieve a temporal resolution way above optical frequencies and thus allows to investigate the energy exchange dynamics between electric fields and matter with unprecedented detail.

    I will discuss how such experiments reveal the influence of electronic correlations on the photoelectric effect and show how solid state attosecond spectroscopy provides us with a time-domain understanding of multi electron dynamics also in solids. These studies observe lasting and transient optical excitations across the band gap of semiconductors and dielectrics with sub-femtosecond response time, the resulting band-structure modifications and the energy exchange dynamics between light-field and solid.

  • Manfred Fiebig

  • Invited speaker: Manfred Fiebig
    Affiliation: ETH Zürich
    Title: Light-Matter Interaction in Ferroic Materials
    Time and room: 17:15, lecture hall IAP
    Abstract: Systems with strong electronic correlations lead to a fascinating variety of phenomena such as magnetic order, multiferroicity, superconductance, colossal magnetoresistance and much more. Well-established characterization methods are at our disposal for investigating these states of matter, including, for example, diffraction techniques, scanning probe microscopy as well as magnetic, dielectric or transport measurements. In my talk, I will focus on the interplay of nonlinear laser spectroscopy and ferroic order. Laser pulses can be used either to monitor ferroic states with spatial (domains) or temporal (dynamics) resolution. On the other hand, strong light pulses can manipulate the ordered state as such and even induce phase transitions.

  • Igor Lesanovsky

  • Invited speaker: Igor Lesanovsky
    Affiliation: University of Nottingham
    Title: Dissipative Spin Systems Far From Equilibrium
    Time and room: 17:15, lecture hall IAP
    Abstract: Cold atomic gases are a versatile platform for the study of quantum many-body phenomena. Especially atoms excited to highly-lying electronic states – so-called Rydberg atoms – offer rather intriguing possibilities for the exploration of strongly correlated dynamics of interacting spin systems.
    I will present recent results which schow that the out-of-equilibrium behaviour of Rydberg gases is governed by emergent kinetic constraints. Such constraints are often used to mimic dynamical arrest or excluded volume effects in idealised models of glass forming substances and lead to a remarkably rich physics including non-equilibrium phase transitions and localisation phenomena. Moreover, Rydberg gases offer intriguing opportunities for the systematic exploration of the role of competing quantum and classical dynamical effects on non-equilibrium phase transitions.
    I will conclude by discussing how the above findings can be employed to gain a new perspective on the physics of Dynamic Nuclear Polarisation in interacting electronic and nuclear ensembles, which is an out-of-equilibrium method to drastically enhance the performance of Magnetic Resonance Imaging applications.

  • Michael Zwerger

  • Invited speaker: Michael Zwerger
    Affiliation: Universität Basel
    Title: Measurement-based Quantum Computation
    Time and room: 17:15, lecture hall IAP
    Abstract: Measurement-based quantum computation is a scheme of quantum computing where the computation is driven by single qubit measurements on entangled resource states.
    The first part of the talk will cover the basic principles of measurement-based quantum computation and an overview over experimental demonstrations. In the second part some recent results from the quantum information group in Innsbruck will be discussed. This includes measurement-based quantum communication, adaptive quantum computation and flexible resources for quantum metrology.