A microwave frequency standard based on trapped, buffer gas-cooled 171Yb+ ions-some accuracy issues

The performance, as characterised by the Allan deviation, of the trapped ¹⁷¹Yb⁺ ion frequency standard NML-IT-2 is equal to or better than σ_y(τ)=6×10^-14 τ^-1/2, for averaging times less than 1000 s. There is evidence that the measured performance is limited both in the short and medium (τ>1000 s) term by the stability of the hydrogen maser used as a frequency reference. A preliminary investigation of the dependence of the observed clock frequency corrected for the calculated second order Doppler shift on the trap conditions has yielded an approximate set of confidence limits on the calculated values of the second order Doppler shift