Cold Atomic Fountain Research Articles

Trapped ion optical frequency standards

Optical frequency standards based on narrow absorptions in laser-cooledsingle trapped ions have recently begun to demonstrate stabilities that arecompetitive with cold atom fountain microwave standards. This paperpresents a short review of the wider state-of-the-art development of thesesingle cold trapped ion frequency standards, coupled with a more detailedaccount of recent results achieved at National Physical Laboratory inrespect of single ion systems based on 88Sr+, 87Sr+ and 171Yb+.Narrow linewidth data for the optical clock quadrupole and octupoletransitions respectively at 674 nm in 88Sr+and 467 nm in 171Yb+, arepresented, together with a discussion of current systematics and futureprojections. The potential for optical clock operation is outlined.

Cavity frequency pulling in cold atom fountains

We present an analytical model and a numerical calculation of the cavity frequency pulling effect in cold atom fountains. We report the first measurement of this effect in a /sup 87/Rb fountain. We find a quantitative agreement with theory.

/sup 87/Rb versus /sup 133/Cs in cold atom fountains: a comparison

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.