LASER-COOLED NEUTRAL ATOM FREQUENCY STANDARDS

Recent advances in laser cooling, including temperatures as low a few microkelvin, and the demonstration of the ability to launch atoms while maintaining these low temperatures, now allows the realization of atomic fountain frequency standards. An analysis of a Cs microwave fountain predicts potential stability and accuracy improvements of a factor of 100 over present laboratory standards, with an ultimate accuracy near 10(-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 current Cs standards, and a possible accuracy of 10(-18). Neutral atom frequency standards will have much better signal-to-noise (S/N) ratios than ion standards, but suffer from larger systematic effects, making the two technologies complementary in many ways.