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Quantum technologies

Dieter Meschede's research group
Home AMO physics colloquia
  • Prof. Jakob Reichel

  • Invited speaker: Prof. Jakob Reichel
    Affiliation: Laboratoire Kastler Brossel de l'ENS
    Title: Miniaturizing cavity QED with Fiber Fabry-Perot cavities
  • T. Kitagawa

  • Invited speaker: Takuya Kitagawa
    Affiliation: Havard University
    Title: Topology in dynamical systems: from quantum walk to graphene
    Abstract: Topological properties of physical systems such as integer quantum Hall systems and topological insulators have attracted attentions due to its universal aspect, where they are insensitive to the details of materials and robust against many perturbations. Such properties resulting from topology are not limited to static systems but extendable to dynamical quantum systems. In this talk, we study periodically driven dynamics and show that such dynamics can have topologically robust behaviors classified by two distinct topological invariants. We demonstrate that such topological properties can be dynamically induced by considering explicit examples with quantum walks and dynamics in graphene.
  • Dr. Eric Lutz

  • Invited speaker: Dr. Eric Lutz
    Affiliation: Universität Augsburg
    Title: Thermodynamics at the Nanoscale
    Time and room: 17 h c.t., lecture hall IAP
    Abstract: We present an overview of recent progress in the thermodynamic description of small systems, emphasizing the crucial role of thermal and quantum fluctuations. We discuss the importance of exact nonequilibrium relations (fluctuation theorem and Jarzynski equality) and their verifications using single-particle experiments. We finally focus on the quantum-mechanical definition of thermodynamic quantities, such as work and energy, and suggest a method to measure them in ultracold ion traps.

  • Prof. Luis Santos

  • Invited speaker: Prof. Luis Santos
    Affiliation: Institut für Theoretische Physik, Universität Hannover
    Title: Ultra-cold Spinor Gases
    Time and room: 17 h c.t., lecture hall IAP
    Abstract: In the last years the physics of ultra-cold spinor gases (atoms with more than two internal degrees of freedom, i.e. spin or pseudo-spin higher than 1/2) has attracted a large interest. In this talk I will first review some of the basic features of ultra-cold spinor gases, and in particular how the interplay between interatomic interactions, Zeeman energy and trapping energy induces a rich physics in these gases, both in what concerns their ground-state phases and the spinor dynamics.

    I will then present some of our recent results on ultra-cold spinor gases. In particular, I will first discuss parametric amplification of spin-vacuum fluctuations in spinor Bose-Einstein condensates.I will then comment on the properties of strongly-correlated fermions in one-dimensional optical lattices. I will specifically show how the quadratic Zeeman effect may induce various types of quantum phase transitions between various magnetic phases of a Mott-insulator of spin-3/2 fermions.

  • Prof. Han Woerdman

  • Invited speaker: Prof. Han Woerdman
    Affiliation: Universität Leiden
    Title: Quantum Entanglement of Orbital Angular Momentum
    Time and room: 17 h c.t., lecture hall IAP
    Abstract: The phase of a light beam can be twisted as a corkscrew around its axis of propagation. Such fields have drawn much attention, in particular since it was realized in 1992 that a twisted light beam carries Orbital Angular Momentum (OAM), namely lħ per photon; here the integer l is the azimuthal mode index of the beam. The concept of OAM has spread into many branches of optics, ranging from optical trapping to quantum information. In optical trapping OAM enables mechanical rotation due to transfer of OAM from light to matter, where the material object can vary from a Bose-Einstein condensate to a living cell. In quantum information OAM allows a high-dimensional alphabet associated with a single photon instead of the usual two-dimensional polarization qubit. Classically speaking, this OAM multiplexing may increase the capacity of a communication channel.

    In the talk I will introduce and compare some of the many methods to produce OAM light beams. This serves as a starting point for the main part of the talk which deals with high-dimensional OAM entanglement of two photons. Particularly interesting is the case that the azimuthal index l of the photon state is non-integer; here the half-integer state plays a special role. Such a state corresponds to a high-dimensional superposition of integer OAM states; it can be easily produced in the lab. Quantifying the dimensionality of bipartite entanglement of these non-integer OAM states requires considerable care; for this purpose we introduce the Shannon dimension, in addition to the better known Schmidt dimension. So far we have demonstrated a Shannon dimension up to 6, and a further increase by an order of magnitude seems possible.