IAP logo UniBonn logo
  • Increase font size
  • Default font size
  • Decrease font size

Quantum technologies

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

  • Prof. M. Prevedelli

  • Invited speaker: Prof. Marco Prevedelli
    Affiliation: Università di Bologna
    Title: Measuring the Gravitational Constant G With Atom Interferometry
    Time and room: 17:15, lecture hall IAP
    Abstract: The gravitational constant G is one of the oldest and yet the least precisely known fundamental physical constants. In spite of 2 centuries of experimental efforts systematic effects still seems to be unsolved problems. In the last 20 years atom interferometry has became a well established experimental technique for realizing sensitive and accurate inertial sensors. A measurement of G using atom interferometry aiming to 100ppm accuracy is in progress in Florence. The experiment combines standard techniques in laser cooling, sometimes with rather stringent requirements, with more unusual, for AMO physics, mechanical requirements. A general overview of the experiment and its present state will be given and few selected experimental problems will be described in deeper detail.
  • M. Karski's defense

  • PhD defense: Michał Karski
    Title: State-selective transport of single neutral atoms
  • Prof. Jakob Reichel

  • Invited speaker: Prof. Jakob Reichel
    Affiliation: Laboratoire Kastler Brossel de l'ENS
    Title: Miniaturizing cavity QED with Fiber Fabry-Perot cavities