New measurement of the rubidium hyperfine frequency using LNE-SYRTE fountain ensemble

We report the operation of LNE-SYRTE FO2 fountain with rubidium 87 after several substantial improvements. With these improvements, FO2-Rb fountain reaches a similar level of performance as LNE-SYRTE cesium fountains with an accuracy of 4.5 parts in 10
¹⁶
. This Rb fountain has been compared to LNE-SYRTE FOM transportable fountain for more than 50 days, down to a resolution <10
^-16
. The Rb hyperfine frequency is measured with a total uncertainty of 1.1 x 10
^-15
.