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Quantum technologies

Dieter Meschede's research group
Home AMO physics colloquia
Colloquia
  • Nir Davidson

    (16/10/17)
  • Invited speaker: Nir Davidson
    Affiliation: Weizmann Institute of Science, Israel
    Title: Normal and Anomalous Diffusion of Atoms in Real Space and Frequency Space

    Time and room: Special Colloquium, from Kaiserslautern. 16:00 h, IAP Conference room
    Abstract: 

    SELECTED
  • David Gross

    (10/10/17)
  • Invited speaker: David Gross
    Affiliation: Universität zu Köln
    Title: Efficient Characterization of High-Dimen-sional Classical and Quantum Problems

    Time and room: 17:15, lecture hall IAP
    Abstract: During the past years, progress in controlling many-body quantum systems has led to the emergence of a new bottle neck: The number of parameters required to fully characterize a system has reached a regime where naive methods are no longer applicable. This is problematic in the emergent field of quantum technologies, where the verification and characterization of components is an important objective. The development is in no way unique to quantum physics. Indeed, classically, the theory of ill-defined high-dimensional estimation problems has become a successful focus of mathematical data science. I'll report in particular on work we have done in the context of "compressed sensing", which bridges the classical and the quantum theories.

  • Peng Xu

    (26/07/17)
  • Invited speaker: Peng Xu
    Affiliation: Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences
    Title: Single-Qubit Operations and Two-Qubit Entanglement with Individually Controlled Neutral Atoms

    Time and room: 10:15, lecture hall IAP
    Abstract: Among various platforms for quantum computing and simulations, trapped neutral atoms offer unique advantages of long coherence time, scaling and excellent control of the interaction strength over 12 orders. However there are still several primary challenges to be solved. In this talk, I will present our recent experimental efforts towards two problems. One is extending single qubit coherence time using magic intensity dipole trap. The other is entangling two heteronuclear single atoms using Rydberg blockade for low crosstalk qubit measurement with a few µm qubit spacing.

  • Jürgen Eschner

    (25/07/17)
  • Invited speaker: Jürgen Eschner
    Affiliation: Universität Saarbrücken
    Title: Single-Photon-Single-Atom Quantum Interfaces

    Time and room: 17:15, lecture hall IAP
    Abstract: We are developing a comprehensive set of experimental tools, based on ion-trapping and photonic technologies, that enable controlled generation, storage, transmission, and conversion of single photonic quantum bits, thereby integrating single photons and single atoms into a quantum network. Specifically, we implemented a programmable atom-photon interface, employing the controlled quantum interaction between a single trapped 40Ca+ ion and single photons [1,2]. Depending on its mode of operation, the interface serves as a bi-directional atom-photon quantum state converter (receiver and sender), as a source of entangled atom-photon states (entangler), or as a quantum frequency converter of single photons [3,4] (converter). It lends itself particularly to integrating ions with single photons or entangled photon pairs from spontaneous parametric down-conversion (SPDC) sources [5,6]. As an experimental application of the receiver mode, we demonstrate the transfer of entanglement from an SPDC photon pair to atom-photon pairs with high fidelity [7]. It is realized by heralded absorption and storage of a single photonic qubit in a single ion. We extend our quantum network toolbox into the telecom regime by quantum frequency conversion of ion-resonant single photons [9], and by implementing telecom-heralded single-photon absorption [5]. In addition, we observe signatures of entanglement between the ion and a single telecom photon. This is obtained after controlled emission of a single photon at 854 nm and its polarization-preserving frequency conversion into the telecom band, by difference-frequency generation in a nonlinear waveguide.

    1. M. Schug et al., Phys. Rev. A 90, 023829 (2014).
    2. P. Müller, J. Eschner, Appl. Phys. B 114, 303 (2014).
    3. C. Kurz et al.,Nat. Commun. 5, 5527 (2014);
    4. C. Kurz et al.,Phys. Rev. A 93, 062348 (2016).
    5. A. Lenhard et al., Phys. Rev. A 92, 063827 (2015).
    6. J. Brito et al., Appl. Phys. B. (2016), 122:36.
    7. S. Kucera et al., in preparation.
    8. N. Sangouard et al., New J. Phys. 15, 085004 (2013).
    9. A. Lenhard et al.,Opt. Express 25, 11187 (2017).

     

  • Sandro Wimberger

    (21/07/17)
  • Invited speaker: Sandro Wimberger
    Affiliation: Università di Parma 
    Title: Discrete-time walks of a Bose-Einstein condensate in momentum space
    Time and room: 09:15, Seminar room I, HISKP 1.021
    Abstract: Each step in a discrete-time quantum walk is typically understood to have two basic components: a „coin-toss“ which produces a random superposition of two states, and a displacement which moves each component of the superposition by different amounts. Here we report on the experimental realization of a walk in momentum space with a spinor Bose-Einstein condensate (BEC) subject to a quantum ratchet realized with a pulsed, off-resonant optical lattice. By an appropriate choice of the lattice detuning, we show how the atomic momentum can be entangled with the internal spin states of the atoms. For the coin-toss, we propose to use a microwave pulse to mix these internal states. We present first experimental results of such a quantum walk based on a new type of ratchet, and through a series of simulations, demonstrate how our system can allow for the investigation of possible biases and classical-to-quantum dynamics in the presence of natural and engineered noise. Moreover, the same setup offers the possibility to realize classical random walks by applying a random sequence of intensities and phases of the time-dependent lattice chosen according to a given probability distribution. This distribution converts on average into the final momentum distribution of the atoms. In particular, it is shown that a power-law distribution for the intensities results in a classical Lévy walk in momentum space. Finally, we propose another implementation of a BEC quantum walk in reciprocal or quasimomentum space with exciting possibilities to investigate the effects of long-range quantum correlations induced by atom-atom interactions.