Uncertainty Budget of Rubidium Fountain: Preliminary Results

The structure, principle of operation, and metrological performance of the rubidium atomic fountain developed at VNIIFTRI are presented. The aim of the present work is to assess the preliminary uncertainty budget of this standard. The physical effects that cause the largest shifts of the measured frequency, namely, the quadratic Zeeman effect, blackbody radiation effect, gravitational redshift, and cavity pulling effect are considered. The frequency stability of the rubidium fountain is given by σ_y(τ) = 1.43·10^–13τ^–1/2 at an evaluated frequency uncertainty of less than 2·10^–16. Such performances are at the level of the best rubidium fountain standards developed worldwide. These results are relevant for the time and frequency metrology and for timescales.