Accurate rubidium atomic fountain frequency standard

Abstract

The design, operating parameters and the accuracy evaluation of the NPL Rb atomic fountain are described. The atomic fountain employs a double magneto-optical arrangement that allows a large number of 87Rb atoms to be trapped, a water-cooled temperature-stabilized interrogation region and a high quality factor interrogation cavity. From the uncertainties of measured and calculated systematic frequency shifts, the fractional frequency accuracy is estimated to be 3.7 × 10−16. The fractional frequency stability, limited predominantly by noise in the local oscillator, is measured to be 7 × 10−16 after one day of averaging. Based on the proposed quasi-continuous regime of operation of the fountain, the accuracy of the Rb standard of 5 × 10−17 reachable in two days of averaging is predicted.

Two-color rubidium fiber frequency standard

“…This approach removes both in-coupling alignment fluctuations along with the need of a vacuum system. This is a route for this platform to achieve frequency stabilities at the level of ≈10 −13 , which would match previously demonstrated Rb two-photon frequency standards [6] and begins to rival the stability of Rb fountain clocks [14] and hydrogen masers.…”

Contributing to TAI with a secondary representation of the SI second

“…Agreement with LNE-SYRTE measurements is claimed at the 10 −15 level but, to our knowledge, the actual result of the measurement has not yet been published [74]- [76].…”

Closely interleaved self-comparison method applied to precise measurement

“…Furthermore, in pursuit of better determination of type-B uncertainties with a particularly small effect and uncertainties hard to obtain directly, the self-comparison method, as a direct evaluation, is widely used. The self-comparison is fulfilled by the same clock running in different states [1,6,[9][10][11][12][13][14][15][16] . Since the method is significant in the removal of systematic errors, it has succeeded in the evaluation of cold collisional frequency shifts of 133 Cs and 87 Rb atomic fountain clocks [1,9,10] .…”

“…The self-comparison is fulfilled by the same clock running in different states [1,6,[9][10][11][12][13][14][15][16] . Since the method is significant in the removal of systematic errors, it has succeeded in the evaluation of cold collisional frequency shifts of 133 Cs and 87 Rb atomic fountain clocks [1,9,10] . Besides, self-comparison is also used in the evaluation of optical lattice clocks, partially due to the lack of comparable clocks [6,[11][12][13][14][15][16] .…”

“…These error signals are used to calculate the relative frequency shift of the physical effect. Our CISC method can bypass the reference clock and extra comparison loops required in other methods [1,9,10] , and leads to better applicability for high precise clocks. The method can also evaluate the uncertainties without interrupting the running of the clock, and provides more information for the Allan deviation at short averaging times due to the close interleaving.…”