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Quantum technologies

Dieter Meschede's research group
Home AMO physics colloquia
  • Ennio Arimondo

  • Invited speaker: Prof. Ennio Arimondo
    Affiliation: Università di Pisa
    Title: Rydberg Excitations Of Condensates
    Time and room: 17:15 lecture hall IAP
    Abstract: Experiments with ultracold atoms enable the quantum simulation of models describing condensed matter phenomena. One major goal is to emulate models, which are believed to underlie certain quantum magnetic materials and high-temperature superconductors. However, in most ultracold atom realizations, thesmall interaction makes the underlying physics extremely challenging to observe. An approach to produce strong long-range interactionsis based on the atomic excitation to Rydberg states experiencing strong long-range dipole-dipole atomic interactions.
     We have investigated the Rydberg excitation in Bose-Einstein condensates of rubidium atoms loaded into quasi one-dimensional traps and in optical lattices.
    The results for condensates expanded to different sizes in the one-dimensional trap agree well with the intuitive picture of a chain of Rydberg excitations. Time-of-flight observations confirmed that the Rydberg excitations in the optical lattice do not destroy the overall phase coherence of the condensate. The observed time dependence of the condensate excitation agrees with the picture of localized collective Rydberg excitations including nearest-neighbor blockade.
     For Rydberg excitations in magneto-optical traps and condensates, we have studied the counting statistics by performing a large number of excitations under the same conditions. The observed highly sub-Poissonian distributions with Mandel Q-factors close to -1 indicate the highly collective character of the Rydberg excitations due to the mean interparticle distance's being much smaller than the dipole blockade radius of the Rydberg states (55 < n < 80) used in our experiments. Our results were compared to numerical simulations using a novel theoretical model based on Dicke states of Rydberg atoms including dipole-dipole interactions, finding good agreement between experiment and theory.

  • Vorstellung des Nobelpreises 2012

  • Ist der Mond auch da, wenn man nicht hinsieht? Von der Paul-Falle zu Schrödingers Katze.

    Anlässlich der Verleihung des Nobelpreises in Physik 2012 an Serge Haroche und David Wineland wird Prof. Meschede die damit gewürdigten Forschungsarbeiten in einem öffentlichen Vortrag vorstellen. Alle Studierenden, Mitarbeiter der physikalischen Institute und an der Physik Interessierten sind herzlich eingeladen.

    Der Vortrag findet am 31. Oktober 2012 um 16:00 Uhr im Wolfgang-Paul-Hörsaal statt.

  • Iacopo Carusotto

  • Invited speaker: Dr. Iacopo Carusotto
    Affiliation: Università di Trento
    Title: Theory And Experiments With Quantum Fluids Of Light
    Time and room: 17:15 lecture hall IAP
    Abstract: A few years after the first observation of Bose-Einstein condensation, quantum gases of dressed photons in semiconductor microcavities (the so-called exciton-polaritons) are a powerful workbench for the study of phase transitions and many-body effects in a novel non-equilibrium context.
    In this talk, I will first briefly review remarkable experiments investigating superfluid hydrodynamics effects in photon fluids hitting localized defects: depending on the flow speed, a wide range of behaviors have been observed, from superfluid flow, to the super-sonic Mach cone, to the nucleation of topological excitations such as solitons and vortices. I will then illustrate recent theoretical studies in the direction of generating strongly correlated photon gases, from Tonks-Girardeau gases of impenetrable photons in one-dimension, to quantum Hall liquids in the presence of artificial magnetic fields.
    Advantages and disadvantages of the different material platforms in view of generating and detecting strongly correlated gases will be reviewed, in particular laterally patterned microcavity and micropillar devices in the optical range, and circuit-QED devices in the microwave domain.

  • Hendrik Ulbricht

  • Invited speaker: Dr. Hendrik Ulbricht
    Affiliation: University of Southampton
    Title: Centre of Mass Motion Interferometry of Molecules and Nanoparticles
    Time and room: 17:15 lecture hall IAP
    Abstract: The motivation for de Broglie interference of heavy particles is manifold, for example, to address the foundations of physics by invesitgating the quantum to classical transition, the use of interferometric techniques for applications such as: molecule metrology, molecule sorting, molecule quantum interference lithography and investigations of van der Walls/Casimir-Polder interactions, and to study the coherent manipulation of complex partciles for instance to reconstruct the Wigner function of the motional quantum state of the diffracted molecules. The centre of mass interferometry is not affected by internal excitation of the molecules as impressively demonstrated by our experiments. If however internal state dynamics is coupled to the centre of mass motion by electric or optical fields, the interference pattern is changed. I will explain our experiment on mapping the dynamics of the change of conformation of hot molecules onto its centre of mass motion while measuring the interference pattern. I will further emphasise the status of the develpoment of the Southampton molecule interferometer, where we recently achieved 27% of quantum contrast.

  • Clive Emary

  • Invited speaker: Dr. Clive Emary
    Affiliation: Institut für Theoretische Physik, TU Berlin
    Title: Distinguishing quantum from classical transport with the Leggett-Garg inequality
    Time and room: 17:15 lecture hall IAP
    Abstract: The Leggett-Garg inequality, often described as a temporal Bell's inequality, sets a bound on the nature of correlations of a single system at different times. Violation of this inequality implies the absence of a macroscopic real, i.e. classical probabilistic, description of the system.

    In this talk I shall introduce the Leggett-Garg inequality and discuss how it can be used to gain insight into whether a transport process operates under classical or quantum-mechanical laws. I will discuss realisations with quantum dots and electron interferometers, as well as make a connection with the theory of full counting statistics.

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