Abstract

The results on accurate measurement of the absolute frequency of the ⁸⁷Rb hyperfine ground-state transition in the NPL Rb fountain frequency standard will be presented. Preliminary frequency measurements of the Rb transition against the new NPL Cs fountain (after the subtraction of the quadratic Zeeman, BBR and gravitational Red shifts) agrees within 5×10⁻¹⁵ with the previous measurements at the BNM-SYRTE dual fountain [1,2] performed in 1999 and 2002. The accuracy of the measurements is expected to be further improved after complete characterisation of all the systematic shifts of the Rb hyperfine clock transition currently in progress.

© 2009 IEEE