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Dieter Meschedes Forschungsgruppe
Home AMO-Physikkolloquien
  • Stefan Brakhane

  • Diplom-Kolloquium: Stefan Brakhane
    Title: Control of Atom-Cavity Coupling using Feedback
    Time and room: 15:15, lecture hall IAP
  • Prof. Michael Drewsen

  • Invited speaker: Prof. Michael Drewsen
    Affiliation: University of Aarhus
    Title: Ion Coulomb Crysal Based Cavity QED Experiments
    Time and room: 09:15, lecture hall IAP
  • Prof. Daniel Hägele

  • Invited speaker: Prof. Daniel Hägele
    Affiliation: Universität Bochum
    Title: Neues von der Photolumineszenz
    Time and room: 17:15, lecture hall IAP

  • Prof. C. Chin

  • Invited speaker: Prof. Chen Chin
    Affiliation: Chicago University
    Title: Observation of Scale Invariance and Universality in Two-Dimensional Quantum Gases
    Time and room: 17:15, lecture hall IAP
    Abstract: The collective behavior of a many-body system near a continuous phase transition is insensitive to the details of its microscopic physics. Characteristic features near the phase transition, called critical phenomena, are that the thermodynamic observables follow generalized scaling laws. The Berezinskii-Kosterlitz-Thouless (BKT) phase transition in two-dimensional Bose gases, for example, presents a particularly interesting case because the marginal dimensionality and intrinsic scaling symmetry result in a broad fluctuation regime which manifests itself in an extended range of scale invariant and universal behavior. We report the observation of a global invariance of scale and a universal description of 2D gases based on direct in situ optical imaging. The extracted universal thermodynamic functions confirm the wide critical regime near the BKT phase transition, provide a sensitive test to Monte Carlo calculations, and point toward a growing density-density correlations in the critical regime. Our observation raises new perspectives to explore further universal phenomena in the realm of quantum critical physics near a quantum phase transition.
  • Dr. Karim Murr

  • Invited speaker: Dr. Karim Murr
    Affiliation: Università di Bologna
    Title: Observation of squeezed light with one atom
    Time and room: 14:15, conference room
    Abstract: For a coherent or vacuum state of the electromagnetic field, the quantum uncertainties of its fluctuating electric and magnetic components are equal and minimize the Heisenberg’s uncertainty relation. It is nowadays possible to reduce the value of one of the uncertainties below the vacuum level at the expense of increasing the other. Such ”squeezed” states are so far generated using macroscopic media only, such as atomic vapours, optical fibres or non-linear crystals.

    That a single atom can produce squeezed light has been predicted almost 30 years ago by Walls and Zoller. However, it has been foreseen by Mandel in 1982 that the squeezing generated by one atom would be “at least an order of magnitude more difficult” to observe than antibunching. Despite experimental efforts, single-atom squeezing has escaped observation.

    We observe squeezed near-infrared light generated by a single neutral atom trapped inside a high-finesse optical cavity. With an excitation beam containing on average only 2 photons per system’s lifetime, the measured field quadratures clearly present a phase-dependent nonclassical response. I will discuss the history on the theory of squeezing as well as the experimental results for an audience knowing only basics on quantum theory.