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Quantum technologies

Dieter Meschede's research group
Home AMO physics colloquia
Colloquia
  • Igor Lesanovsky

    (13/06/17)
  • 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

    (30/05/17)
  • 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.
     

  • Matthias Keller

    (16/05/17)
  • Invited speaker: Matthias Keller
    Affiliation: University of Sussex
    Title: Interfacing Ions and Photons
    Time and room: 17:15, lecture hall IAP
    Abstract: The complementary benefits of trapped ions and photons as carriers of quantum information make it appealing to combine them in a joint system. Ions provide low decoherence rates, long storage times and high readout efficiency, while photons travel over long distances. To interface the quantum states of ions and photons efficiently, we use calcium ions coupled to an optical high-finesse cavity via a Raman transition.
    To achieve strong ion-cavity coupling we employ fibre tip cavities integrated into the electrodes of an endcap style ion trap. With a cavity length of 380 mm the resulting ion-cavity coupling strength is 17 MHz with a cavity line width of 10 MHz. We trap single calcium ions with a life time of several hours and have optimised the ion-cavity overlap to observe the interaction of the cavity with the ion.
    In another experiment, we combine a conventional cavity with a linear ion trap to facilitate the investigation of the interaction of multiple ions with a single cavity mode. We have demonstrated the localisation of several ions in a collinear cavity-trap system and have demonstrated the emission of polarised single photons from this system.
    To enable the use of fibre cavities in applications such as single photon sources and nodes in quantum networks the coupling between the cavity and the fibre must be significantly improved. We have developed a system to integrate mode matching optics into a fibre system and have demonstrated a mode matching between cavity and fibre on the order of 90%.
     

    SELECTED
  • Wilhelm Zwerger

    (10/05/17)
  • Invited speaker: Wilhelm Zwerger
    Affiliation: TU München
    Title: Have Ultracold Atoms Led to Progress in Theoretical Physics?
    Time and room: 10:15, lecture hall HISKP
    Abstract: Ultracold atoms have opened new directions in physics, both by realizing paradigmatic models in many-body and statistical physics and by allowing to explore phenomena which have never been accessible before. In this talk, I will discuss to which extent ultracold atoms have also triggered new developments in theoretical physics.
    It is shown that for the quantum many-body problem with zero range interactions which appears naturally in the context of ultracold atoms, there are a number of exact relations which connect the short distance behavior of the one- and two-body density matrix with thermodynamic properties and also the high-frequency or large momentum behavior of correlation functions. These relations follow from a Wilson operator product expansion and thus apply to arbitrary states of the many-body system. Two examples for their concrete application are given: the violation of scale invariance in RF-spectroscopy of two-dimensional Fermi gases and deep inelastic scattering on strongly interacting Bose gases at large momentum.

  • Franz Gie├čibl

    (09/05/17)
  • Invited speaker: Franz J. Gießibl
    Affiliation: Universität Regensburg
    Title: Progress in Studying Matter on the Atomic Scale
    Time and room: 17:15, lecture hall IAP
    Abstract: The scanning tunneling microscope (STM), invented in 1981 by Binnig and Rohrer, has provided direct access to the world of atoms. STM relies on vacuum tunneling with an exponential increase of a tunneling current between two biased conductive electrodes at a factor of ten per Å. If a tip has one atom that sticks out one Å more than all the others, this front atom carries ten times more current than the other atoms. The monotonic decrease of current with distance facilitates distance feedback and allows to scan the tip across a sample with atomic precision. In 1986, Binnig, Gerber and Quate introduced atomic force microscopy (AFM), a method that also images insulators by relying on forces. Unlike the current, the force between tip and sample is non-monotonic and includes long- and short range components. AFM has been inferior in resolution to STM for a long time. Today, it exceeds STM in spatial resolution. That progress was enabled by advances in measuring small forces and by the isolation of chemical bonding forces from strong background forces.


    Figure: AFM image of an Fe3 and Fe2 cluster on a Cu(111) surface.