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Transport et relaxation d'atomes de césium : oscillations de Bloch et résonance de diffusion

Abstract : In this thesis, we have studied quantum effects with ultracold cesium atoms. We describe first an experiment using atoms, laser-cooled down to 10 nanoKelvin, in a periodic optical potential. At this temperature, atoms are delocalized over several periods of the potential. Such a system appears to be a powerful tool to study properties of coherent quantum transport. We have observed Bloch oscillations of atoms. This quantum effect has been introduced for electrons in the frame of solid state physics. It states that particles in a periodic potential have an oscillatory motion when submitted to a constant force. We also show that the dynamics of the Bloch Oscillations are equivalent to a sequence of adiabatic rapid passage and demonstrate a novel technique of coherent acceleration of atoms. These results may find applications in atom optics and precision measurement. In the second part of this work, we have studied properties of magnetically trapped cold atoms. By investigating relaxation of the cloud towards thermal equilibrium, we infer that the s wave elastic cross section varies as 1/T between 5 and 60 μK. It takes at each measured temperature the maximum allowed value for polarized bosons. This indicates a zero-energy resonance generated by a bound or virtual state close to the dissociation threshold. In terms of the triplet scattering length a, it leads to a lower bound for |a| equal to 260 a0, significantly higher than for other alkali atoms. Such an observation should have important consequences for evaporative cooling of cesium clouds.
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  • HAL Id : tel-00011913, version 1

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Maxime Ben_dahan. Transport et relaxation d'atomes de césium : oscillations de Bloch et résonance de diffusion. Physique Atomique [physics.atom-ph]. Université Pierre et Marie Curie - Paris VI, 1997. Français. ⟨tel-00011913⟩

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