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Quantum technologies

Dieter Meschede's research group
Home AMO physics colloquia
Colloquia
  • David Hunger

    (24/01/17)
  • Invited speaker: David Hunger
    Affiliation: LMU München
    Title: Quantum- and Nanooptics with Tunable Microcavities  

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

    Spatio-temporal confinement of light can dramatically enhance light-matter interactions. To achieve this capability on an accessible platform, we have developed microscopic Fabry-Perot cavities based on laser-machined optical fibers [1].
    We employ such cavities to realize efficient and narrow-band single-photon sources by means of Purcell enhancement of fluorescence emission. We study color centers in diamond such as the Nitrogen-Vacancy center [2] and explore different regimes of the cavity enhancement, aiming at applications in quantum cryptography, all-optical quantum computation, and efficient spin-state readout.
    In the context of sensitive microscopy, we use microcavities for imaging and spectroscopy applications. We have developed scanning cavity microscopy as a versatile method for spatially and spectrally resolved maps of various optical properties of a sample with ultra-high sensitivity. We demonstrate the technique by quantitative imaging of the extinction cross-section of gold nanoparticles and measurements of the birefringence and extinction contrast of gold nanorods [3]. Finally, we show that the Purcell effect can be used for cavity-enhanced Raman spectroscopy and hyperspectral imaging [4]. Simultaneous enhancement of absorptive, dispersive, and scattering signals promises intriguing potential for optical studies of nanomaterials, molecules and biological nanosystems.

    [1] D. Hunger et al., New J. Phys. 12, 065038 (2010)
    [2] H. Kaupp et al., Phys Rev Applied 6, 054010 (2016)
    [3] M. Mader et al., Nature Commun. 6, 7249 (2015)
    [4] T. Hümmer et al., Nature Commun. 7, 12155 (2016)

  • Hendrik Bluhm

    (17/01/17)
  • Invited speaker: Hendrik Bluhm
    Affiliation: RWTH Aachen
    Title: Semiconductor Spin Qubits - From Proof of Principle Demonstrations to High Fidelity Quantum Gates  

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

    Qubits based on electron spins trapped in fabricated semiconductor nanostructures such as gate controlled quantum dots or individual donors are considered promising candidates for scalable solid state quantum computing, which promises an exponential speedup for certain computational tasks.
    Starting from an outline of the development of key concepts, I will give a (selective) overview of the current state of the art of GaAs and Si based spin qubit devices. Key results include single shot readout, high fidelity single-qubit manipulation, and first demonstrations of two-qubit gates. One particular focus of my talk will be effects from the hyperfine interaction of nuclear spins with the electron spin qubit, which is a source of strong decoherence when present and unavoidable in GaAs devices. The intricate physics emerging from hyperfine coupling is now rather well understood and we have developed effective methods to reduce the associated dephasing and achieve high fidelity qubit control.

  • Yoichi Ando

    (10/01/17)
  • Invited speaker: Yoichi Ando
    Affiliation: Universität zu Köln

    Title: Topological Insulators and Superconductors  

    Time and room: exceptionally:  17:30 h, lecture hall IAP

    Topological insulators and superconductors are new quantum states of matter that are characterized by nontrivial topological structures of the Hilbert space [1]. Recently, they attract a lot of attention because of the appearance of exotic quasiparticles such as spin-momentum-locked Dirac fermions or Majorana fermions on their surfaces, which hold promise for various novel applications [2]. In this talk, I will introduce the basics of those materials and present some of the key contributions we have made in this new frontier.
    [1] Y. Ando, Topological Insulator Materials, J. Phys. Soc. Jpn. 81, 102001 (2013).
    [2] Y. Ando and L. Fu, Topological Crystalline Insulators and Topological Superconductors: From Concepts to Materials, Annu. Rev. Condens. Mater Phys. 6, 361 (2015).
     

  • Florian Marquardt

    (13/12/16)
  • Invited speaker: Florian Marquardt
    Affiliation: Universität Erlangen-Nürnberg
    Title: Light, Sound, and Topology 

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

    In this talk, I will first give a brief introduction to the field of cavity optomechanics, where one couples radiation fields
    to the motion of mechanical resonators. I will then explain how optomechanical interactions can be exploited to modify the transport
    of phonons and photons in two-dimensional arrays of coupled optical and vibrational modes. These can e.g. be implemented in photonic crystal slabs.
    Engineering the light field wave front, it is possible to generate a topologically nontrivial bandstructure via the optomechanical interaction.
    This gives rise to transport of sound waves along chiral edge channels that are robust against disorder. In the last part of the talk, I will
    indicate how one can even use a purely geometrical nanoscale design for chiral sound wave transport in a pseudo-magnetic field.

    "Topological Phases of Sound and Light"
    Vittorio Peano, Christian Brendel, Michael Schmidt, and Florian Marquardt, Phys. Rev. X 5, 031011 (2015)

    "Pseudomagnetic fields for sound at the nanoscale"
    Christian Brendel, Vittorio Peano, Oskar Painter, and Florian Marquardt, arXiv:1607.04321 (2016)
     

  • Per Delsing

    (06/12/16)
  • Invited speaker: Per Delsing
    Affiliation: Chalmers University of Technology, Göteborg
    Title:  Quantum Optics with Microwaves and Superconducting Circuits 

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

    Recently it has become possible to do quantum optics experiments, where propagating microwaves interact with artificial atoms in the form of superconducting circuits [1]. In our case, the artificial atoms are made from transmon qubits, where we utilize also the higher levels of the transmon. In this colloquium I will discuss several such experiments.In the first set of experiments, we embed a transmon artificial atom in an open transmission line. When a weak coherent state is on resonance with the atom, we observe extinction of >99% in the forward propagating field. Addressing the higher levels, it is possible to observe the Autler-Towns splitting, and the Mollow triplet. Using the Autler-Towns splitting we demonstrate how photons can be routed efficiently and fast on-chip [2]. By applying a control tone, we also observe a giant cross-Kerr effect [4]. Furthermore we study the statistics of the reflected and transmitted radiation and we demonstrate antibunching in the reflected field and superbunching of the transmitted field.
    In a second set of experiments, we embed a transmon at a distance from the end of an open transmission line, which acts as a mirror[5]. By tuning the wavelength of the atom, we effectively change the normalized distance between atom and mirror, allowing us to effectively move the atom from a node to an antinode of the vacuum fluctuations. We probe the strength of vacuum fluctuations by measuring spontaneous emission rate of the atom.
    [1] I.-C. Hoi et al. New Journal of Physics 15, 025011 (2013)
    [2] I.-C. Hoi et al. Physical Review Letters 107, 073601 (2011)
    [3] I.-C. Hoi et al. Physical Review Letters 108, 263601 (2012)
    [4] I.-C. Hoi et al. Physical Review Letters 111, 053601 (2013)
    [5] I.-C. Hoi et al. Nature Physics, 11, 1045 (2015)