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Quantum technologies

Dieter Meschede's research group
Home AMO physics colloquia
  • Thomas Zentgraf

  • Invited speaker: Prof. Thomas Zentgraf
    Affiliation: Universität Paderborn
    Title: Generalized Snell's Law: Interaction of Light with Artificial Surfaces

    Time and room:  17:15 h, lecture hall IAP
    Abstract: Optical applications and components very often rely on refraction at geometrically shaped interfaces between two materials or spatial modulation of the phase during the propagation of light. Both effects, however, require a variation of the refractive index in three-dimensional space and lead to optical elements that need to be significantly thicker than the utilized wavelength. Recently, new approaches with, artificially structured materials, the so-called Metamaterials, opened new possibilities for the realization of compact optical elements. The high degree of flexibility in the design and manufacture of optical Metamaterials allows now to control the propagation of light to a high degree. Plasmonic Metasurfaces that consist only of a monolayer of planar metal structures are in particular promising. They have the advantage that they can provide full control over light propagation with relatively low manufacturing costs and no requirements on complex three dimensional nano fabrication techniques. One of the most interesting properties of Metasurfaces is the ability to produce an abrupt phase change for the passage of light through a surface. This phase change offers a unique possibility for controlling the local wave front on a sub wavelength scale which also leads to a modification of the classic law of refraction. The talk will provide an overview of the concept of Metasurfaces and show recent developments in the field of beam shaping and holography.

    Figure: Projection of a holographic image from a nanostructured surface hologram.

  • Xavier Marie

  • Invited speaker: Prof. Xavier Marie
    Affiliation: Université Toulouse
    Title: Introducion To 2D Semiconductors Based On Transition Metal Dichalcogenides (MoS2, MoSe2, WS2, WSe2)

    Time and room:  17:15 h, lecture hall IAP
    Abstract: The spectacular progress in controlling the electronic properties of graphene has triggered research in alternative atomically thin two-dimensional crystals. Monolayers (ML) of transition-metal dichalcogenides such as MoS2 have emerged as very promising nanostructures for optical and electronic applications for mainly two reasons.
    First, the indirect bulk semiconductor MoS2 becomes direct when thinned to 1ML, resulting in efficient optical absorption and emission. Second, inversion symmetry breaking (usually absent in graphene) together with the large spin-orbit interaction leads to a coupling of carrier spin and k-space valley physics, i.e., the circular polarization (σ+ or σ−) of the absorbed or emitted photon can be directly associated with selective carrier excitation in one of the two nonequivalent k valleys (K+ or K−, respectively).
    In this talk I will give an overview of the physical properties of 2D semiconductors based on Transition Metal Dichalcogenides : band structure, exciton effects, optical and transport properties, and spin/valley dynamics.

  • Francesca Ferlaino

  • Invited speaker: Prof. Francesca Ferlaino
    Affiliation: Universität Innsbruck
    Title: Dipolar Physics with Ultracold Atomic Magnets

    Time and room:  17:15 h, lecture hall IAP
    Abstract: Given their strong magnetic moment and exotic electronic configuration, rare-earth atoms disclose a plethora of intriguing phenomena in ultracold quantum physics. Here, we report on the first degenerate Fermi gas of erbium atoms, based on direct cooling of identical fermions via dipolar collisions [1]. We study the impact of the anisotropic character of the interaction following the re-thermalization dynamics of a dipolar Fermi gas driven out of equilibrium [2]. At the many-body level, we prove the long-standing prediction of a deformed Fermi surface in dipolar gas [3]. Finally, scattering experiments show a spectacularly high number of Fano-Feshbach resonances. This complexity, arising from the anisotropy of the interactions, escapes to traditional scattering models and requires novel approaches based on statistical analysis. Using the powerful toolset provided by Random-Matrix theory, we elucidate the chaotic nature of the scattering [4].

    [1] K. Aikawa, A. Frisch, M. Mark, S. Baier, R. Grimm, and F. Ferlaino, 
Phys. Rev. Lett. 112, 010404 (2014).
    [2] K. Aikawa, A. Frisch, M. Mark, S. Baier, R. Grimm, J. L. Bohn, D. S. Jin, G. M. Bruun, F. Ferlaino Phys. Rev. Lett. 113, 263201 (2014).
    [3] K. Aikawa, S. Baier, A. Frisch, M. Mark, C. Ravensbergen, F. Ferlaino, Science 345, 1484 (2014)
    [4] A. Frisch, M. Mark, K. Aikawa, F. Ferlaino, J. L. Bohn, C. Makrides, A. Petrov, and S. Kotochigova, Nature 507, 475-479 (2014).

  • Tracy Northup

  • Invited speaker: Dr. Tracy Northup
    Affiliation: Universität Innsbruck
    Title: An Ion-cavity Interface for Quantum Networks

    Time and room: 17:15 h, lecture hall IAP
    Abstract: Trapped ions are a promising platform for local quantum information processing, while optical cavities offer a coherent interface between matter and light, enabling the transfer of quantum information from stationary qubits onto photons for long-distance distribution.

    We demonstrate such an interface by coupling trapped ions to a cavity and have recently shown that a quantum state can be faithfully transferred from an ion onto a photon. In particular, this transfer can be improved by taking advantage of a collective effect between multiple ions, namely, superradiant emission into the cavity. In this proof-of-principle experiment, we tune the phase of a two-ion entangled state between sub- and superradiance. The superradiant coupling is then used to enhance the transfer of quantum information onto a photon from a logical qubit encoded in the two ions.

    Finally, prospects for linking together distant ions in cavities via a quantum network will be discussed. Toward this goal, I will outline a fiber-based ion-cavity experiment designed to access the single-ion strong-coupling regime.

  • Yaron Silberberg

  • Invited speaker: Prof. Yaron Silberberg
    Affiliation: Weizmann Institute of Sciences, Rehovot, Israel
    Title: Wavefront Shaping: Controlling Light in Complex Media

    Time and room: special colloquium, 14:15 h, lecture hall IAP
    Abstract: The propagation of light in inhomogeneous media, such as biological tissues and the turbulent atmosphere, results in wavefront distortion and scattering, which imposes a major limitation in many applications. Examples range from microscopy and nanosurgery to astronomy. In addition to the frequently encountered spatial distortions, multiple-scattering also randomly distorts the polarization state of the incident light, and its temporal and spectral characteristics. However, although multiple-scattering is a random process, it is a deterministic one and it can be undone. I shall review the growing field of wavefront shaping and describe how, using a single spatial light modulator, one can control and correct the spatial, temporal, spectral and polarization distortions in random media. I shall demonstrate schemes for nonlinear imaging behind scattering layers, and for seeing 'around corners'.

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