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Quantum technologies

Dieter Meschede's research group
Home AMO physics colloquia
  • Christophe Salomon

  • Invited speaker: Christophe Salomon
    Affiliation: CNRS, Ecole Normale Supérieure, Paris
    Title: Single-Qubit Operations and Two-Qubit Entanglement with Individually Controlled Neutral Atoms

    Time and room: 17:15, lecture hall IAP
    Abstract: We report on the production and study of a mixture of Bose and Fermi superfluids.
    Such a mixture has long been sought in liquid helium where superfluidity was achieved separately in bosonic 4He and fermionic 3He. However due to strong interactions between isotopes, phase separation occurs when the 3He concentration exceeds 6%, which, so far, has prevented reaching simultaneous superfluidity for both species.
    Using dilute quantum gases where interactions can be tuned, we have produced a Bose-Fermi mixture where both species are superfluid [1]. By exciting center of mass oscillations of the mixture we probe the collective dynamics of the system. Coherent energy exchange between the Bose and Fermi gas is observed with very small damping below a certain critical velocity. We compare this critical velocity for superfluid counterflow to a recent theoretical prediction [2,3]. Raising the temperature of the system slightly above the superfluid transition reveals an unexpected phase-locking of the oscillations induced by dissipation. Finally the lifetime of the Bose-Fermi mixture is governed by a very simple formula involving the fermionic two-body contact [4].

    1. Igor Ferrier-Barbut, Marion Delehaye, Sebastien Laurent, Andrew T. Grier, Matthieu Pierce, Benno S. Rem, Frédéric Chevy, Christophe Salomon, A Mixture of Bose and Fermi Superfluids, Science 345, 1035, (2014)
    2. Y. Castin, I. Ferrier-Barbut, and C. Salomon, The Landau critical velocity for a particle in a Fermi superfluid, Comptes Rendus Physique, 16, 241 (2015).
    3. M. Delehaye, S. Laurent, I. Ferrier-Barbut, S. Jin, F. Chevy, and C. Salomon, Critical Velocity and Dissipation of an ultracold Bose-Fermi Counterflow, Phys. Rev. Lett., 115, 265303 (2015).
    4. S. Laurent, M. Pierce, M. Delehaye, T. Yefsah, F. Chevy, C. Salomon, Connecting few-body inelastic decay to quantum correlations in a many-body system : a weakly coupled impurity in a resonant Fermi gas, Phys. Rev. Lett., 118, 103403 (2017)

  • Nir Davidson

  • 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

  • David Gross

  • 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

  • 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

  • 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).


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