Laser-cooled neutral atom frequency standards

The authors review the prospects for a frequency standard based on what is called the atomic fountain. Atomic fountain frequency standards have better signal-to-noise ratios than ion standards, but suffer from larger systematic effects. An analysis of a Cs microwave fountain predicts potential stability and accuracy improvements of a factor of 100 over other laboratory standards, with an ultimate accuracy near 10/sup -16/. An optical frequency standard based on a two-photon transition in xenon is analyzed and shown to have potential stability 5 orders of magnitude better than conventional Cs standards, and a possible accuracy of 10/sup -18/. Neutral atom frequency standards will have much better signal-to-noise ratios than ion standards, but suffer from larger systematic effects, making the two technologies complementary in many ways.<
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