title: (87)Rb versus (133)Cs in cold atom fountains: a comparison.
abstract: We describe the operation of a laser cooled (87)Rb frequency standard and present a new measurement of the (87)Rb ground state hyperfine frequency with a relative accuracy of 2.4x10(-15), by comparison with a Cs fountain primary standard. The measured frequency is 6 834 682 610.904 333(17) Hz. An evaluation of the frequency shift induced by cold collisions gives Deltanu/nu(Rb)=(-7.2+/-20)x10(-24) n , where n is the average atomic density in cm(-3). With our present 1 sigma uncertainty of 10(-15), this measurement is still compatible with 0 and about 300 times smaller than for (133)Cs. We also report a test of a possible variation of the fine structure constant at the level of 2.7x10(-14) yr(-1), comparing Rb and Cs cold atom fountains.
authors.affiliation: Lab. Primaire du Temps et des Frequences, Paris.
authors.forename: Y
authors.initials: Y
authors.lastname: Sortais
authors.forename: S
authors.initials: S
authors.lastname: Bize
authors.forename: C
authors.initials: C
authors.lastname: Nicolas
authors.forename: G
authors.initials: G
authors.lastname: Santarelli
authors.forename: G C
authors.initials: GC
authors.lastname: Salomon
authors.forename: A
authors.initials: A
authors.lastname: Clairon