A microwave frequency standard in the 10^–15 accuracy range using ¹⁷¹Yb+ ions

National Measurement Laboratory, CSIRO, Sydney

3.30pm, Friday 7 March 2003, AR103 Seminar Room, Graduate Research Centre

Microwave frequency standards of the highest stability and accuracy have been under development at CSIRO’s National Measurement Laboratory (NML) for a number of years. The reference frequency of these standards is the ground state hyperfine interval Δv of the ¹⁷¹Yb+ ion, analagous to the interval for ¹³³Cs which presently defines the SI second. In recent years, work at NML has concentrated on the use of laser cooling to reduce or eliminate systematic shifts while preserving the exceptional stability already demonstrated by ion-trap standards. To date we have measured Δv = 12 642 812 118.468 5(7)(6) Hz, where the two uncertainties relate to comparisons from the ions to a hydrogen maser and from the maser to the SI second respectively. The accuracy is presently limited only by technical issues such as the homogeneity of the magnetic field. With a redesigned non-magnetic UHV trap chamber, we expect an accuracy of 4x10^–15 or better, comparable to the best Cs fountain standards operating today. Though our primary interest is metrology, such a standard also opens up various possibilities for tests of fundamental physics.

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