Preliminary Evaluation of the Cesium Fountain Primary Frequency Standard NMIJ-F2

Abstract

We describe the preliminary evaluation of the frequency corrections and their uncertainty in the cesium fountain primary frequency standard (PFS) NMIJ-F2 under development at National Metrology Institute of Japan (NMIJ). In NMIJ-F2, cold atoms generated from a vapor-loaded optical molasses in the (001) configuration are optically pumped to the Zeeman sublevels of m F = 0 to increase the number of atoms involved in the Ramsey interrogation. Moreover, a cryocooled sapphire oscillator with ultralow phase noise is employed as the local oscillator to avoid degradation of the frequency stability due to the Dick effect. As a result, we have obtained a very high fractional frequency stability of 9.7 × 10 −14 τ −1/2 . As for systematic frequency shifts, the fractional correction for the second-order Zeeman shift is experimentally estimated to be (−165.5 ± 0.5) × 10 −15 from the first-order Zeeman shift of atoms in m F = +1 launched to various heights. The fractional frequency correction for cold-atom collisions is estimated to be (+3.3 ± 0.4) × 10 −15 by extrapolating the frequency to zero density from the frequencies measured for various nonzero atom numbers. We will soon be able to make a comparison with other atomic fountain PFSs at the 1 × 10 −15 level.Index Terms-Atomic fountain clock, primary frequency standard (PFS), uncertainty evaluation.

Demonstration of the nearly continuous operation of an171Yb optical lattice clock for half a year

“…As demonstrated in previous experiments that utilized continuously running fountain clocks and hydrogen masers [73], the continuous operation contributes to reduce the statistical uncertainty in a relatively short term, resulting in a stringent limit on violation of local position invariance. In our case, this experiment can be carried out by comparing the Yb clock with a local Cs fountain clock [74] that transient variations of the fine structure constant resulting from the passage of dark matter may be observed in a global network of optical clocks [24]. The detection of the transient effects relies on correlations in the frequency data of worldwide clocks running simultaneously [75].…”

State Preparation in a Cold Atom Clock by Optical Pumping

“…This technique was adopted in NMIJ-F2 as well. [10] The design scheme of NIM6 also proposed a depumping-optical pumping procedure, allowing the state selection microwave cavity to be removed. [11] From another perspective, the time for loading cold atoms can be decreased to only a fraction of the original value with this method.…”

Improvement of the short-term stability of atomic fountain clock with state preparation by two-laser optical pumping*

“…[9,10] And now, OP has also been used in the atomic fountain clocks with π-polarized laser to accumulate atoms in the |m F = 0 state. [11][12][13][14][15] A theoretical model of evaluating the pumping efficiency, taking into account of ground and excited states structures, Zeeman coherences, neighboring transitions, and laser field fluctuations, has been presented in Ref. [16].…”

“…[12] by collecting atoms with a magneto-optical trap (MOT) and in the Ref. [15] by collecting atoms with an optical molasses (OM) in atomic fountain clocks.…”