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Frequency shift due to blackbody radiation in a cesium atomic fountain and improvement of the clock performances

Abstract : FO1 was the first caesium fountain primary frequency standard in the world. The most recent evaluation in 2002 before improvement reached an accuracy of 1x10^-15 when operated with optical molasses. Working as an extremely precise and stable instrument, FO1 has contributed to fundamental physics and technical measurements: - Frequency comparison between Cs and Rb fountains over an interval of 5 years sets an upper limit for a possible variation of the fine structure constant as |alpha/alpha|< 2x10^-15 yr^-1. The resolution is about 5 times better than the previous test in our laboratory. - The projected accuracy of the space clock PHARAO is 1x10^-16. We confirmed its Ramsey cavity performance by testing the phase difference between the two interaction zones in FO1. - The measured temperature T dependent frequency shift of the Cs clock induced by the blackbody radiation field is given as nu(T)=154(6)x10^-6(T/300)^4[1+epsilon(T/300)^2] Hz with the theoretical value epsilon=0,014. The obtained accuracy represents a 3 times improvement over the previous measurement by the PTB group. Some improvements have been carried out on FO1. The new FO1 version works directly with optical molasses loaded by a laser slowed atomic beam. The application of the adiabatic passage method to perform the state selection allows us to determine the atom number dependent frequency shifts due to the cold collision and cavity pulling effects at a level of of 10^-16. Recently, the obtained frequency stability is 2,8x10^-14 tau^-1/2 for about 4x10^6 detected atoms. The accuracy is currently under evaluation, the expected value is a few times 10^-16.
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Submitted on : Sunday, October 10, 2004 - 12:56:56 PM
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  • HAL Id : tel-00007074, version 1

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Shougang Zhang. Frequency shift due to blackbody radiation in a cesium atomic fountain and improvement of the clock performances. Atomic Physics [physics.atom-ph]. Université Pierre et Marie Curie - Paris VI, 2004. English. ⟨tel-00007074⟩

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