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Quantum technologies

Dieter Meschede's research group
Home AMO physics colloquia
Colloquia
  • Fabian Grusdt

    (06/04/17)
  • Invited speaker: Dr. Fabian Grusdt
    Affiliation: Harvard University
    Title: Quantum impurities in strongly correlated phases of ultracold atoms
    Time and room: 17:15, lecture hall IAP
    Abstract: The detection and control on the level of individual lattice sites achieved by experiments with ultracold atoms and photons allows for new measurements which are difficult to realize using traditional solid-state setups. This makes such systems ideal candidates to explore exotic phases of matter, including the fractional quantum Hall effect or high-temperature superconductors. An overview will be given of the recent progress towards reaching this goal with cold atom quantum simulators. The main theme of this talk are mobile quantum impurities inside the strongly correlated quantum systems described above. On the one hand, impurities can be used as coherent probes of the many-body system. Specifically I will show how topological invariants can be measured in a fractional quantum Hall setup in this way. In other cases, impurities are at the heart of the many-body problem itself: For example, the high-temperature superconducting phase is obtained by doping mobile holes into a Mott insulator with anti-ferromagnetic spin correlations. A simple physical theory of a single hole in such systems will be presented.

  • David Weiss

    (21/03/17)
  • Invited speaker: Prof. David Weiss
    Affiliation: Pennsylvania State University
    Title: What does it take for a closed quantum system to thermalize?
    Time and room: 17:15, lecture hall IAP
    Abstract: An integrable many-body system has as many conserved quantities are particles. I will explain how these extra constraints keep such a system from thermalizing in a conventional way. One dimensional gases of neutral atoms are nearly integrable quantum many-body systems. I will describe how we make and study these 1D gases, and how we are trying to use them to understand the fundamental limits of statistical mechanics.

  • Peter Knott

    (16/02/17)
  • Invited speaker: Peter Knott
    Affiliation: Fraunhofer-Institut für Hochfrequenzphysik und Radartechnik
    Title: RADAR Systems – Technology and Challenges  

    Time and room:  13:30 h, lecture hall IAP

    During the last decade, numerous developments have not only improved and matured technology and signal processing methods of RADAR systems, but also paved the road for many new applications besides its traditional domains in defence and space. The rapid progress in performance of highly integrated electronic components (digital, analogue or mixed-signal) has enabled several trends such as miniaturisation and cost reduction of sensor devices, a migration to higher frequencies in the millimetre and Terahertz domain, or real-time execution of mathematically complex signal and array processing methods. On the other hand, the electromagnetic spectrum is a scarce and strongly controlled resource that is proving to be increasingly valuable. Radar devices must be able to handle more signal bandwidth with greater receiver sensitivity and are competing with an increasing number of other systems for communication, navigation, or wireless connectivity. In this environment, it is necessary to understand the different requirements and find strategies of a co-existence without performance degradation.
    The presentation gives an overview of recent developments at Fraunhofer FHR and application examples such as airborne and ground based surveillance, Digital Beam Forming AESA systems, or Cognitive Radar Architecture.

  • Jan Klaers

    (07/02/17)
  • Invited speaker: Jan Klaers
    Affiliation: ETH Zürich
    Title: A Minimalist Nano-mechanical Engine Beyond the Carnot Limit  

    Time and room:  17:30 h, lecture hall IAP

    Heat engines, as employed in cars, ships and airplanes, are everyday examples showing that heat can produce directed motion. The efficient conversion of thermal energy to mechanical work by an engine is, however, an ongoing technological challenge. Since the pioneering work of Carnot, it is known that the efficiency of engines is bounded by a fundamental upper limit ‑ the Carnot limit. Nowadays, micro- and nanotechnological methods allow to test thermodynamics far away from the thermodynamic limit. Highly miniaturized forms of heat engines have been experimentally realized, where the working medium is represented by a single particle instead of 10^23 particles as in the macroscopic world. Theoretical studies suggest that the efficiency of such engines may overcome the standard Carnot limit by employing stationary, non-equilibrium reservoirs that are characterized by a temperature as well as further parameters, for example, quantum coherent, quantum correlated and squeezed thermal reservoirs. In a proof-of-principle experiment, we demonstrate that the efficiency of a minimalist nano-mechanical heat engine coupled to squeezed thermal noise is not bounded by the standard Carnot limit. Furthermore, a cycle process can be realized that allows to extract mechanical work from a single squeezed thermal reservoir. These results quantitatively test our understanding of non-equilibrium thermodynamics at small scales and provide a new perspective on the design of efficient, highly miniaturized engines.

    SELECTED
  • Tommaso Roscilde

    (31/01/17)
  • Invited speaker: Tommaso  Roscilde
    Affiliation: ENS Lyon
    Title: Quantum correlations: Where are they? How do they build up? How to measure them? 

    Time and room:  17:15 h, lecture hall IAP

    When a system is composed of many parts, "more is different" (as P. W. Anderson famously wrote) if and only if there are correlations among the various parts. If the constituents are quantum mechanical atoms, spins, oscillators, etc., "more" can be even "more different", as correlations can take forms which are impossible in classical mechanics. The most famous, yet elusive form of quantum correlation is represented by entanglement, a property well defined and investigated for pure states, and envisioned as a resource for nearly all technological tasks harnessing quantum many-body systems. In the real life of mixed states incoherent fluctuations appear in the game, making the distinction of quantum vs. classical correlations less sharp. At the same time, the exquisite level of control achieved by experiments in atomic, molecular and optical (AMO) physics enables nowadays to engineer correlated phases of quantum many-body systems, so that the ability to characterize and control quantum correlations becomes a fundamental question, as well as (possibly) a technological one.
    In this colloquium I will try to offer a broad overview of the theoretical importance of quantum correlations, starting from their very definition - to which we contributed recently with a statistical physics approach which allows to calculate them in generic systems, and potentially to measure them for a large class of quantum many-body systems relevant to experiments in AMO physics and beyond. I will moreover discuss the centrality of quantum correlations in the dynamics that leads a closed quantum system to relax to an equilibrium state, contrasting the case of short-range interactions with that of long-range ones: this contrast allows to enlighten the role of elementary excitations (and in particular of their dispersion relation) as the "carriers" of quantum correlations.