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Quantum technologies

Dieter Meschede's research group
Home AMO physics colloquia
Colloquia
  • Benoît Darquié

    (22/01/13)
  • Invited speaker: Dr. Benoît Darquié,
    Affiliation: Université Paris 13
    Title: High-Resolution Molecular Spectroscopy In The Mid-IR – Precision Measurements
    And Tests Of Fundamental Physics
    Time and room: 17:15 lecture hall IAP
    Abstract: Accurate molecular spectroscopy in the mid-infrared region allows precision measurements with applications in metrology or fundamental physics. I will report on some of our latest results on the determination of the Boltzmann constant kB by Doppler spectroscopy and on the search for a parity violation effect in chiral molecules.
    Measuring the linewidth of an isolated Doppler-broadened absorption line of ammonia around 10 μm enables a determination of kB. By fitting this lineshape to several models which include Dicke narrowing and speed-dependent collisional effects, we find that a determination of kB with an uncertainty of a few ppm is reachable. This is comparable to the current uncertainty obtained using acoustic methods and would make a significant contribution to any new value of kB determined by the CODATA. Furthermore, having multiple independent measurements at these accuracies opens the possibility of defining the kelvin by fixing kB, an exciting prospect considering the upcoming redefinition of the International System of Units.
    Parity violation (PV) effects have so far never been observed in chiral molecules. Originating from the weak interaction, PV should lead to frequency differences in the rovibrational spectra of the two enantiomers of a chiral molecule. However the weakness of the effect represents a very difficult experimental challenge. We propose to compare the rovibrational spectra (around 10 μm) of two enantiomers, recorded using the ultra-high resolution spectroscopy technique of Doppler-free two-photon Ramsey interferometry in a supersonic molecular beam. With an alternate beam of left- and right-handed molecules and thanks to our expertise in the control of the absolute frequency of the probe CO2 lasers, we should reach a fractional sensitivity better than 10-15, on the frequency difference between enantiomers. We will review our latest results on the high-resolution spectroscopy, either in cell or in a supersonic beam, of methyltrioxorhenium, an achiral test molecule from which our collaborators are currently synthesizing chiral derivatives fulfilling all the requirements for the PV test.

  • Carsten Klempt

    (15/01/13)
  • Invited speaker: Dr. Carsten Klempt
    Affiliation: Universität Hannover
    Title: Entangled Matter Waves For Sub-Shot-Noise Interferometry
    Time and room: 17:15 lecture hall IAP
    Abstract: Matter wave optics with ultracold samples has reached the point where nonclassical states can be prepared and their fascinating properties can be explored. In optics, parametric down-conversion in nonlinear crystals has become one of the standard methods to generate entangled states of light. The rapid progress in the preparation and manipulation of ultracold neutral atomic gases now allows for the realization of such entangled states with matter waves.
    Bose-Einstein condensates of atoms with non-zero spin provide a mechanism analogous to parametric down-conversion. The presented process acts as a two-mode parametric amplifier and generates two clouds with opposite spin orientation consisting of the same number of atoms. We show a two-fold spontaneous breaking of spatial and spin symmetries, which is deeply connected to two-mode squeezing.

    At a total of 10000 atoms, we observe a squeezing of the number difference of -7 dB below shot noise, including all noise sources. As a first application, we demonstrate that the created state is useful for precision interferometry. We show that its interferometric sensitivity beats the standard quantum limit, the ultimate limit of unentangled states. The created states of matter can be employed in future atom interferometers to improve the sensitivity of gyroscopes, accelerometers, gravity sensors or atomic clocks.

  • Uwe Fischer

    (18/12/12)
  • Invited speaker: Prof. Uwe Fischer
    Affiliation: Seoul National University
    Title: Employing Collapse And Revival Oscillations For The Analysis Of Quantum Many-Body States
    Time and room: 17:15 lecture hall IAP
    Abstract:  We argue that forcing an interacting quantum many-body system to reside
    after a quench far from its equilibrium state, is an important tool to reveal information on the correlations in the initial ground state. We discuss two examples in detail:

    [1] We investigate the collapse and revival of first-order coherence in deep optical lattices when long-range interactions are turned on and find that the first few revival peaks are strongly attenuated already for moderate values of the nearest-neighbor interaction coupling. It is shown that the conventionally employed Gutzwiller wavefunction, with only on-site number dependence of the variational amplitudes, leads to incorrect predictions for the collapse and revival oscillations within the extended Bose-Hubbard model. We provide a modified variant of the Gutzwiller ansatz, reproducing the analytically calculated time dependence of first-order coherence in the limit of zero tunneling.

    [2] We consider the rapid quench of a one-dimensional strongly correlated supersolid to a localized density wave (checkerboard) phase, and calculate the first-order coherence signal following the quench. It is shown that unique coherence oscillations between the even and odd sublattice sites of the checkerboard are created by the quench, which are absent when the initial state is described by a Gutzwiller product state. This is a striking manifestation of the versatility of the far-from-equilbrium and nonperturbative collapse and revival phenomenon as a microscope for quantum correlations in complex many-body states. For the present example, this opens up the possibility to discriminate experimentally between mean-field and many-body origins of supersolidity.

  • Antoine Browaeys

    (11/12/12)
  • Invited speaker: Prof. Antoine Browaeys
    Affiliation: Institut d'Optique, Paris
    Title: Experimental Investigation Of The Dipole-Dipole Interaction
    Time and room: 17:15 lecture hall IAP
    Abstract: This talk will present our ongoing effort to understand and use the dipole-dipole interaction between ultra-cold atoms. This dipole interaction can result from the interaction of the atoms with near-resonant light. In this case the scattering of light by  an ensemble of atoms is modified if the inter-atomic distance is on the order of the wavelength of the light. The atoms then behave collectively, leading to super or sub-radiant phenomena. The dipoles can also be prepared by exciting the atoms to a Rydberg state leading to interaction strength large enough to make the atoms interact even at long distance. This Rydberg interaction is at the basis of the preparation of entangled states.

  • Ed Hinds

    (07/12/12)
  • Plücker Lecture 2012
    Invited speaker:
    Prof. Dr. Ed Hinds
    Affiliation: Imperial College London
    Title: Is The Electron Round? Searching For The Electron’s Electric Dipole Moment
    Time and room: 16:15 h, Wolfgang-Paul-Hörsaal
    Abstract: According to the standard model, the charge distribution of the electron has a dipole moment de=10–38 e x cm — eleven orders of magnitude below the current experimental limit. However, most extensions to the standard model predict much larger values, potentially accessible to measurement. Hence, the search for the electron EDM is a search for new particle physics. We have measured de using a molecular beam technique. By measuring atto-eV energy shifts in the YbF molecule, this experiment probes new physics at the tera-eV energy scale. I will describe our experimental method, our current results and their implications for particle physics. I will also consider the prospects for further major improvement in sensitivity.


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