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Dieter Meschedes Forschungsgruppe
Home AMO-Physikkolloquien
  • Hendrik Weimer

  • Invited speaker: Hendrik Weimer
    Affiliation: Universität Hannover
    Title: Quantum Many-Body Dynamics of Driven-Dissipative Rydberg Gases

    Time and room: 17:15, lecture hall IAP
    Abstract: Ultracold Rydberg atoms provide an ideal testbed for study the interplay between strong coherent interactions and dissipative processes, a subject that has recently seen great attention following the discovery of dissipative state engineering for tailored many-body quantum states. However, in contrast to their fully coherent counterparts, our insights into dissipative many-body dynamics are still in its infancy. I will present the first steps towards a deeper understanding of driven-dissipative Rydberg gases based on a recently developed variational principle [1] as well as numerical simulations based on tensor network operators [2]. Specifically, I will investigate phase transitions of the steady state, including the presence of a multicritical point that is triggered by the dissipation within the system [3].

    [1] H. Weimer, Phys. Rev. Lett. 114, 040402 (2015)
    [2] A. Kshetrimayum, H. Weimer, R. Orus, arXiv:1612.00656 (2016)
    [3] V. R. Overbeck, M. F. Maghrebi, A. V. Gorshkov, H. Weimer, Phys. Rev. A 95, 042133 (2017)

  • 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.