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Quantum technologies

Dieter Meschede's research group
Home AMO physics colloquia
  • Michael Johanning

  • Invited speaker: Dr. Michael Johanning                             
    Affiliation: Universität Siegen
    Title: Scalable Quantum Information Processing in ion traps using MAGIC
    Time and room:  17:15 h, lecture hall IAP

    Ion traps are one of the promising platforms for quantum information processing and many proof of principle experiments have been realized with laser cooled trapped ions. A recent development is the application of inhomogeneous magnetic fields and microwave radiation for selective coherent manipulation and conditional dynamics. This allows for long coherence times and high fidelity one and two qubit gates, as demonstrated recently.

    In this talk, I will focus on the storage, manipulation and readout of qubits encoded in the spin degree of freedom which can interact, upon application of an additional magnetic field gradient, by a magnetic gradient induced coupling (MAGIC). I will illustrate the concepts using results obtained with macroscopic and micro-structured traps, and compare to atomic qubits manipulated by optical means.

  • Hans Peter Büchler

  • Invited speaker: Prof. Hans Peter Büchler
    Affiliation: Universität Stuttgart
    Title: Strongly Interacting Rydberg Slow Light Polaritons

    Time and room:  17:15 h, lecture hall IAP

    Synthetic quantum materials offer an exciting opportunity to explore quantum many-body physics and novel states of matter under controlled conditions. In particular, they provide an avenue to exchange the short length scales and large energy scales of the solid state for an engineered system with better control over the system Hamiltonian, more accurate state preparation, and higher fidelity state readout. Here we propose a unique platform to study quantum phases of strongly interacting photons. We introduce ideas for controlling the dynamics of individual photons by manipulating the geometry of a multimode optical cavity, and combine them with recently established techniques to mediate strong interactions between photons using Rydberg atoms. We demonstrate that this approach gives rise to crystalline- and fractional quantum Hall- states of light, opening the door to studies of strongly correlated quantum many-body physics in a photonic material.

  • Wolfgang Schleich

  • Invited speaker: Prof. Wolfgang Schleich
    Affiliation: Universität Ulm
    Title: The Riemann Zeta Function and Quantum Mechanics

    Time and room:  17:15 h, lecture hall IAP

    The Riemann zeta function ζplays a crucial role in number theory as well as physics. Indeed, the distribution of primes is intimately connected to the non-trivial zeros of this function. We briefly summarize the essential properties of the Riemann zeta function and then present a quantum mechanical system which when measured appropriately yields ζ. We emphasize that for the representation in terms of a Dirichlet series interference [1] suffices to obtain ζ. However, in order to create ζ along the critical line where the non-trivial zeros are located we need two entangled quantum systems [2]. In this way entanglement may be considered the quantum analogue of the analytical continuation of complex analysis.

    [1] R. Mack, J. P. Dahl, H. Moya-Cessa, W.T. Strunz, R. Walser and W. P. Schleich, Riemann ζ-function from wave packet dynamics, Phys. Rev. A. 82, 032119 (2010).

    [2] C. Feiler and W.P. Schleich, Entanglement and analytical continuation: an intimate relation told by the Riemann zeta function, New J. Phys. 15, 063009 (2013).

  • Christine Silberhorn

  • Invited speaker: Prof. Christine Silberhorn
    Affiliation: Universität Paderborn
    Special Colloquium
    Title: Sum frequency generation for quantum applications

    Time and room: Thursday, April 28, 2016, Conference Room (311) IAP

    In recent years sum frequency conversion processes have become an established tool to implement quantum information transfer interfaces between systems of different wavelengths. Such interfaces are essential for the realization of quantum networks, which combine different individual components with incompatible frequencies. In particular, long distance quantum communication, which uses stationary qubits with transitions in the visible or UV and flying qubits at telecommunication wavelengths rely on practical quantum frequency converters. Here, we present our work on the realization of sum frequency generation processes from telecommunication regime to visible and UV wavelengths and discuss cw and pulsed light characteristics

  • Copy of Giovanni Barontini

  • Invited speaker: Dr. Giovanni Barontini
    Affiliation:  University of Birmingham
    Title: Strong Coupling Regime In Fibre Microcavities: From EIT To Multi-Particle Entanglement

    Time and room:  17:15 h, lecture hall IAP

    I will report on recent results obtained with cold atoms in fibre microcavities at Imperial College London and at the Laboratoire Kastler-Brossel in Paris. In the London experiment, we show how the Hamiltonian eigenstates of the system can be revealed through spectroscopic measurements despite the fast decoherence rate of the microcavity. We observe an avoided crossing in the dressed cavity spectrum, usually taken as evidence of strong coupling, notwithstanding the complete overdamping of Rabi oscillations in our experiment. We interpret this as dipole-induced transparency of the cavity, relying on destructive quantum interference to uncover the normal modes which might be expected to lie obscured [1]. In the Paris experiment instead, the atom-cavity coupling rate greatly exceeds every loss rate allowing to reach the single-atom strong coupling regime and to perform almost non-destructive measurements. Building on this we have developed a method based on the quantum Zeno dynamics to create symmetric entangled states in ensembles of several tens of atoms. We characterize the resulting states by performing quantum tomography, yielding a time-resolved account of the entanglement generation. In addition, we study the dependence of quantum states on measurement strength and quantify the depth of entanglement. Our results show that quantum Zeno dynamics can be used as a versatile tool for fast and deterministic entanglement generation [2].
    [1] Y.-H. Lien, G. Barontini, M. Scheucher, J. Goldwin, and E. A. Hinds, in preparation
    [2] G. Barontini, L. Hohmann, F. Haas, J. Estéve, and J. Reichel, Science 349, 1317 (2015)