Population and Phase Coherence during the Growth of an Elongated Bose-Einstein Condensate

We study the growth of an elongated phase-fluctuating condensate from a non-equilibrium thermal cloud obtained by shock-cooling. We compare the growth of the condensate with numerical simulations, revealing a time delay and a reduction in the growth rate which we attribute to phase fluctuations. We measure the phase coherence using momentum Bragg spectroscopy, and thereby observe the evolution of the phase coherence as a function of time. Combining the phase coherence results with the numerical simulations, we suggest a simple model for the reduction of the growth rate based on the reduction of bosonic stimulation due to phase fluctuations and obtain improved agreement between theory and experiment

Inhibition of Transport of a Bose-Einstein Condensate in a Random Potential

We observe the suppression of the 1D transport of an interacting elongated Bose-Einstein condensate in a random potential with a standard deviation small compared to the typical energy per atom, dominated by the interaction energy. Numerical solutions of the Gross-Pitaevskii equation reproduce well our observations. We propose a scenario for disorder-induced trapping of the condensate in agreement with our observations.Comment: Proceedings of the 17th International Conference on Laser Spectroscopy (ICOLS 05), Cairngorms National Park, Scotland, 19-24 June 200

An accurate optical lattice clock with 87Sr atoms

We report a frequency measurement of the 1S0-3P0 transition of 87Sr atoms in an optical lattice clock. The frequency is determined to be 429 228 004 229 879 (5) Hz with a fractional uncertainty that is comparable to state-of-the-art optical clocks with neutral atoms in free fall. Two previous measurements of this transition were found to disagree by about 2x10^{-13}, i.e. almost four times the combined error bar, instilling doubt on the potential of optical lattice clocks to perform at a high accuracy level. In perfect agreement with one of these two values, our measurement essentially dissipates this doubt

Temporal coherences of atomic chaotic light sources: the Siegert relation and beyond

Light is characterized by its electric field, yet quantum optics has revealed the importance of monitoring photon-photon correlations at all orders. We here present a comparative study of two experimental setups, composed of cold and warm Rubidium atoms, respectively, which allow us to probe and compare photon correlations up to the fourth order. The former operates in the quantum regime where spontaneous emission dominates, whereas the latter exhibits a temperature-limited coherence time. While both setups present almost-chaotic light statistics, we discuss how the access to different orders of photon correlations allows one to better characterize the mechanisms responsible for deviations from those statistics

Combined spectroscopy and intensity interferometry to determine the distances of the blue supergiants P Cygni and Rigel

In this paper, we report on the spatial intensity interferometry measurements within the H$\alpha$ line on two stars: the Luminous Blue Variable (LBV) supergiant \PCygni\,and the late-type B supergiant Rigel. The experimental setup has been upgraded to allow simultaneous measurement of two polarization channels and the zero baseline correlation function. Combined with simultaneous spectra measurements and based on radiative transfer models calculated with the code CMFGEN, we were able to fit our measured visibility curves to extract the stellar distances. Our distance determinations for both \PCygni\ (1.61 $\pm$ 0.18 kpc) and Rigel (0.26 $\pm$ 0.02 kpc) agree very well with the values provided by astrometry with the Gaia and Hipparcos missions, respectively. This is the first successful step towards extending the application of the Wind Momentum Luminosity Relation method for distance calibration from an LBV supergiant to a more normal late-type B supergiant

Etude des propriétés de cohérence d'un condensat de Bose-Einstein à l'équilibre et hors équilibre

A. Aspect : Directeur de thèse, P. Bouyer : Membre invité, P. Chavel : Président, M. Inguscio : Rapporteur, R. Kaiser : Rapporteur, P. Lemonde : Examinateur, H. Perrin : ExaminatriceThe Bose-Einstein condensate, the atomic counterpart to laser in optics, is usually considered as a fully coherent object. However this is true for systems of moderate anisotropy only. For highly elongated condensates, phase fluctuations appear along the long axis, and these imply a reduction of the coherence length. Such a phase fluctuating condensate is called a quasi-condensate. In this thesis, we report on two experimental studies about the coherence of highly elongated condensates. The first study has been realized on condensates at equilibrium. The measurement of the coherence length has been done through the measurement of the correlation function using an interferometric method. Our results show the transition between a full phase coherent condensate and a quasi-condensate, the coherence length decreasing when the amplitude of the phase fluctuations is increased. We have also observed that the expected shape of the correlation function changes from a Gaussian-like shape to an exponential-like shape. The second study focuses on the formation of the condensate, and more particularly on the kinetic of the establishment of the phase coherence. Our results show that the growth of the condensed fraction proceeds qualitatively as for 3D non-phase-fluctuating condensates. Finally, we have measured the coherence length during the formation using Bragg spectroscopy. Our results show a fast establishment of the coherence compared to the time needed for the condensed fraction to reach equilibrium.Le condensat de Bose-Einstein, équivalent atomique du laser en optique, est habituellement considéré comme un objet complètement cohérent. Mais ceci n'est vérifié que dans le cas de systèmes peu anisotropes. Pour des condensats fortement allongés, des fluctuations de phase apparaissent suivant l'axe long, ce qui implique une réduction de la longueur de cohérence de ces condensats. On parle alors de quasi-condensat. Dans ce mémoire, nous présentons deux études expérimentales portant sur la cohérence de condensats très allongés. La première étude a été réalisée sur des condensats à l'équilibre. La mesure de la longueur de cohérence a été effectuée par l'intermédiaire de la mesure de la fonction de corrélation à l'aide d'une méthode interférométrique. Nos résultats montrent la transition entre un condensat cohérent et un quasi-condensat, avec une longueur de cohérence diminuant avec l'augmentation de l'amplitude des fluctuations de phase. Nous avons par ailleurs observé le passage d'une forme gaussienne à une forme exponentielle pour la fonction de corrélation. La deuxième étude a porté sur la formation du condensat avec plus particulièrement l'étude de la cinétique de formation de la cohérence en phase. Nos résultats montrent tout d'abord une montée de la fraction condensée qualitativement identique à celle des condensats 3D sans fluctuation de phase. Enfin, nous avons mesuré la longueur de cohérence au cours de cette formation à l'aide de la spectroscopie de Bragg. Nos résultats montrent un établissement de la cohérence rapide comparé au temps de mise à l'équilibre de la fraction condensée

Erratum: Limits on nonlinear electrodynamics

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Erratum: Limits on nonlinear electrodynamics

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Erratum: Limits on nonlinear electrodynamics

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The vacuum magnetic birefringence experiment : a test for quantum electrodynamics

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