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Dieter Meschedes Forschungsgruppe
Home AMO-Physikkolloquien
  • Calarco

  • Invited speaker: Tommaso Calarco
    Affiliation: Universität Ulm
    Title: Quantum Technologies and Quantum Control

    Time and room: 17:15, lecture hall IAP
    Abstract: The control of quantum states is essential both for fundamental investigations and for technological applications of quantum physics. In quantum few-body systems, decoherence arising from interaction with the environment hinders the realization of desired processes. In quantum many-body systems, complexity of their dynamics further makes state preparation via external manipulation highly non-trivial. An effective strategy to counter these effects is offered by quantum optimal control theory, exploiting quantum coherence to dynamically reach a desired goal with high accuracy even under limitations on resources such as time, bandwidth, and precision. In this talk I will:
    - introduce the quantum optimal control method we developed to this aim, the CRAB (Chopped Random Basis) algorithm, which is to date the only method that allows to perform optimal control of quantum many-body systems;
    - present experimental results obtained via its application to various physical systems, from quantum logical operations in solid-state quantum optics to quantum criticality in ultra-cold atoms, both in open-loop and in closed-loop feedback scenarios, with applications ranging from quantum interferometry with Bose-Einstein condensates on atom chips to magnetic field sensing in diamond NV centers and to the preparation of optical-lattice quantum registers for quantum simulation;
    - use these examples to illustrate the quantum speed limit, i.e. the maximum speed achievable for a given quantum transformation, and describe related effects of nonlinearity due to inter-particle interactions and more in general to dynamical complexity;
    - propose a way to characterise the latter in an information-theoretical fashion by the bandwidth of the optimized control pulses, as well as a conjecture about using this method for discrimination between different levels of complexity in quantum many-body systems.

  • Hannes Pfeifer

  • Special Colloquium
    Invited speaker:
    Hannes Pfeifer
    Affiliation: Max-Planck-Institut für die Physik des Lichts, Erlangen
    Title:  Optomechanical Crystals for Arrays  

    Time and room: 10:30 h, seminar room IAP
    Abstract: Within the last decade cavity optomechanical systems have dramatically advanced in the exploration of the quantum nature of mechanical oscillators. Ground state cooling, coherent optical to mechanical state transfer and the preparation of non-classical mechanical states are just a few examples of the progress in the experimental control of these systems. Some of the recent challenges in the field are the exploitation of optomechanical cavities as a storage for quantum information and for quantum operations and the realization of networks and arrays of optomechanical cavities.
    One of the platforms that promisingly tackles these problems are optomechanical crystals. Different structures can thereby access a wide range of experimental parameters, still preserving a small footprint due to their on-chip integration. Their challenging fabrication however requires robust designs and/or means to compensate slight structural deviations. After a brief general introduction of optomechanical crystals, this talk will reveal a design for tunable optomechanical nanobeams that can enable phononic networks and a potential solutions for a 2D cavity for low temperature quantum optomechanics.

  • Wirth

  • Invited speaker: Steffen Wirth
    Affiliation: MPI for Chemical Physics of Solids, Dresden
    Title: STM Spectroscopy on Correlated Topological Materials

    Time and room: 17:15, lecture hall IAP

  • Genes

  • Invited speaker: Claudiu Genes
    Affiliation: MPI Erlangen

    Time and room: 17:15, lecture hall IAP

  • Eschrig

  • Invited speaker: Matthias Eschrig
    Affiliation: Royal Holloway University, London
    Title: New Avenues toward Complex Pairing States

    Time and room: 17:15, lecture hall IAP
    Abstract: Current challenges of quantum many-body theory include correlated super-conductivity, topological materials, non-equilibrium phenomena, and complexity at surfaces and interfaces. In particular, the physics near interfaces and surfaces has attracted attention, as it can lead to phases of matter that might not be realized in bulk materials. The increase in functionality due to spin-triplet pairing states in devices has led to the new field of superconducting spintronics.
    Of particular interest are effects based on the presence of gemetric phases and on topological stability. Whereas the former open new avenues toward spin control, the latter have recently attracted strong interest due to their robustness with respect to surface disorder. Spin triplet pairing states in bulk materials can be realized in superfluid 3He, in some correlated super-conductors, or in non-centrosymmetric superconductors. Spin-orbit locking in non-centrosymmetric materials may lead to topological superconductivity giving rise to topologically protected surface Andreev states.
    I will present self-consistent calculations for topological superconductivity in non-centrosymmetric materials, and for superfluid order in 3He in the presence of spin-active surfaces.