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Refroidissement Raman et vols de Lévy: Atomes de césium au nanoKelvin

Abstract : Subrecoil laser cooling of free atoms leads to temperatures which are limited only by the available interaction time. This thesis presents in its first part a theory of subrecoil cooling using Lévy flight statistics, which is tested by Monte Carlo simulations and applied to the technique of Raman cooling. This work shows the importance of the cooling pulse shape and gives the first quantitative expression for the lowest temperature that can be obtained with good efficiency in a given time. In particular, for one-dimensional cooling, simple square pulses are more efficient than the Blackman pulses used previously. Furthermore, it is shown how theory and simulations can be used to obtain the optimum cooling parameters, such as pulse lengths and detunings.

These new results are applied in a one-dimensional Raman cooling experiment using caesium atoms. The all-diode-laser setup includes a magneto-optical trap in a vapour cell and two lasers phase-locked with a frequency difference of 9.19 GHz to drive the Raman transitions. Using square pulses, the experiment leads to a 1D temperature of 2.8 nK with a tenfold increase in peak height with respect to the initial distribution. Still lower temperatures down to 0.8 nK are obtained with slightly reduced peak height. These are to our knowledge the lowest temperatures achieved in laser cooling. At these temperatures, the atomic wave function is delocalized over more than 10 optical wavelengths.

Applications of such an extremely cold atomic sample range from the observation of Bloch oscillations of atoms in a periodic optical potential to improvement of atomic fountain clocks. Subrecoil cooling of trapped atoms is a promising approach to the production of quantum degenerate gases using solely optical techniques.
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Contributor : Jakob Reichel <>
Submitted on : Monday, February 16, 2004 - 4:49:19 PM
Last modification on : Thursday, December 10, 2020 - 12:37:13 PM
Long-term archiving on: : Friday, April 2, 2010 - 8:20:19 PM

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  • HAL Id : tel-00004691, version 1

Citation

Jakob Reichel. Refroidissement Raman et vols de Lévy: Atomes de césium au nanoKelvin. Physique Atomique [physics.atom-ph]. Université Pierre et Marie Curie - Paris VI, 1996. Français. ⟨tel-00004691⟩

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