The measurement of the 87Rb ground-state hyperfine splitting in an atomic fountain

The new atomic Rb-Cs fountain should confirm the recent theoretical calculations relating to the collisions of rubidium atoms. According to this theory, the displacement of the frequency of clock due to the collisional shift was predicted to be 15 times lower for Rb-87 than for Cs-133 at equal density. Using Rb instead of Cs in a fountain standard may lead to an order of magnitude improvement in frequency stability togheter with an excellent accuracy. In this paper we describe the operation of a laser cooled Rb-87 frequency standard and present a nem measurement of the Rb-87 ground state hyperfine frequency with a relative accuracy of 2.4 10(-15) by comparison with a Cs fountain atomic standard In order to measure this, first we determined the absolute frequency of the reference H-maser by comparison with the LPTF's Cs fountain. Second, we corrected the measured frequency to take into account different systematic shifts: magnetic field, black body, microwave leakage, collisions. The measured frequency is 6 834 682 610.903 333 (17) Hz This value differs from previously published values(1,2) by about 2-3 Hz and is 10(4) times more accurate.