Evaluation of the primary frequency standard NPL-CsF1

Szymaniec, K.; Chałupczak, W.; Whibberley, Peter; Lea, S. N.; Henderson, David W.

doi:10.1088/0026-1394/42/1/007

Cited by 73 publications

(78 citation statements)

References 25 publications

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“…This treatment is similar to that reported in [5]. In contrast, we do not use the uncertainty of the axis intercept to estimate uncertainty due to nonlinearity, because the slope is important for estimation of the collisional shift while the vertical displacement of the fitted line is not.…”

Section: B Collisional Shiftmentioning

confidence: 92%

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

Takamizawa

Yanagimachi

Tanabe

et al. 2015

IEEE Trans. Instrum. Meas.

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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.

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Section: B Collisional Shiftmentioning

confidence: 92%

“…Based on the method described in [5], the second-order Zeeman shift averaged over the interrogation time is estimated. At first, the OP is turned OFF, and the atoms in m F = +1 are prepared by adjusting the frequency of the microwave signal in the state-selection cavity.…”

Section: Evaluation Of the Frequency Corrections A Second-order Zmentioning

confidence: 99%

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

Takamizawa

Yanagimachi

Tanabe

et al. 2015

IEEE Trans. Instrum. Meas.

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“…Today, fountains realize the second with a relative accuracy ranging from 3×10 -16 to 10×10 -16 [1][2][3][4][5][6][7] and, in the last ten years, allowed the uncertainty of the Atomic International Timescale (TAI) unit to be reduced from 1×10 -14 to 5×10 -16 . Since 2003, INRIM operates the Cs fountain ITCs-F1 and evaluates on a regular basis the TAI unit with a type B uncertainty of 5×10 -16 and an overall uncertainty less than 1×10 -15 [8].…”

Section: Introductionmentioning

confidence: 99%

Bayesian inference of a negative quantity from positive measurement results

Calonico

Levi

Lorini

et al. 2009

2009 IEEE International Frequency Control Symposium Joint With the 22nd European Frequency and Time Forum

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In this paper Bayesian analysis is applied to a Cesium fountain frequency standard to estimate the density shift correction and its uncertainty. Cesium fountain frequencystandards realize the second in the International System of Units with a relative uncertainty approaching 10 -16 . Among the main contributions to the accuracy budget, cold collisions play an important role because of the so called atomic density shift of the reference atomic transition. The Bayes theorem allows the a priori knowledge of the sign of the collisional correction that is definitively negative to be rigourously embedded into the analysis. In the H-maser frequency measurements using INRIM Cesium fountain as reference, we used the Bayesian analysis and we report a reduction on the final combined uncertainty by more than 25% that demonstrates the Bayesian analysis as a relevant tool in primary frequency-metrology.I.

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“…The setups, already described in detail earlier [17,18] operate in cyclic modes: 10 7 -10 8 Cs atoms from a room temperature vapor are collected and cooled in a MOT. The atoms are then launched in moving optical molasses and further cooled.…”

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confidence: 99%

Cancellation of the Collisional Frequency Shift in Caesium Fountain Clocks

et al. 2007

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We have observed that the collisional frequency shift in primary caesium fountain clocks varies with the clock state population composition and, in particular, is zero for a given fraction of the |F = 4, m F = 0〉 atoms, depending on the initial cloud parameters. We present a theoretical model explaining our observations. The possibility of the collisional shift cancellation implies an improvement in the performance of caesium fountain standards and a simplification in their operation. Our results also have implications for test operation of fountains at multiple π/2 pulse areas. The primary caesium clocks have increased their accuracy and stability by an order of magnitude over the last decade [1]. This staggering progress has mainly resulted from the implementations of laser cooling and the fountain configuration. Slow atoms allow for long interrogation times and observation of narrow resonances (≤ 1 Hz) leading to improvements in the short-term stability. At the same time many systematic effects, which limited the performance of thermal beam clocks, have been significantly reduced in the fountains resulting in improvements of their accuracy. The use of ultracold atoms gave rise, however, to a frequency shift due to collisions, an effect generally neglected in thermal beam clocks. For the several operational fountain frequency standards, the collisions constitute one of the major systematic effects limiting the standards' performance. Generally, the fountain standards are corrected for the collisional frequency shift by extrapolating the measured frequency to zero atom density, assuming a linear dependence between the shift and the density. However, the atomic density is not measured directly in the fountains. The changes in the density are derived from changes in the number N at of detected atoms. A potential deviation from linearity between N at and the atomic density (and hence the shift) gives rise to an uncertainty of the correction. One way to minimize this uncertainty is to operate the fountain at a very low density [2]. Unfortunately, with a low atom number the detection signal-to-noise ratio (and short-term stability of the standard) is reduced. Another way relies on the implementation of a technique based on adiabatic passage to link unambiguously changes in density with changes in N at [3]. In this case, the accuracy of the collisional shift measurement is ultimately limited by a residual amount of atoms in |F = 3, m F ≠ 0〉 colliding with atoms in the clock states during the ballistic flight [4]. Ways of cancelling the collisional shift have been studied earlier. The cancellation would be possible if the cross-sections of the frequency changing collisions of the two clock states |3,0〉 and |4,0〉 were of opposite sign. Then, if a certain composition of the clock states were excited the two contributions to the clock shift would cancel. In the 1990s the relevant cross-sections for various Cs isotopes were calculated and it was shown that the

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Evaluation of the primary frequency standard NPL-CsF1

Cited by 73 publications

References 25 publications

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

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

Bayesian inference of a negative quantity from positive measurement results

Cancellation of the Collisional Frequency Shift in Caesium Fountain Clocks

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