Roadmap towards the redefinition of the second

[redundant material in this field can't be deleted(?)]In this letter we examine the organization of the traditional base units and defining constants established in the 2019 redefinition of the International System of Units (SI). For the next redefinition of the SI, which will accompany the anticipated redefinition of the candela and second, we propose an organizational change to improve clarity while maintaining practicality. We propose three distinct categories of units: The first category contains only the four base-measurement units comprised of the second, meter, kilogram, and ampere. The second category contains physiologically-relevant derived units. The third category contains the remaining units derived from the base units.

Section: A Proposalmentioning

confidence: 99%

A proposal for three categories of units within the SI

Lehman,

Migdall,

Scherschligt

et al. 2024

“…Optical frequency ratio measurements have a vital role to play in verifying the international consistency of optical clocks at a level better than 5 × 10 −18 , one of the criteria set out in the international roadmap towards the redefinition of the SI second [102]. In the 2021 update to the recommended frequency values, the rules and criteria previously employed by the WGFS were modified to ensure that the output data from the least-squares adjustment includes a complete set of frequency ratio values (including absolute frequencies as a special case) that are internally self-consistent.…”

Section: Discussionmentioning

confidence: 99%

The CIPM list ‘Recommended values of standard frequencies’: 2021 update

Margolis,

Panfilo,

Petit

et al. 2024

Self Cite

This paper gives a detailed account of the analysis underpinning the 2021 update to the list of standard reference frequency values recommended by the International Committee for Weights and Measures (CIPM). This update focused on a subset of atomic transitions that are secondary representations of the second (SRS) or considered as potential SRS. As in previous updates in 2015 and 2017, methods for analysing over-determined data sets were applied to make optimum use of the worldwide body of published clock comparison data. To ensure that these methods were robust, three independent calculations were performed using two different algorithms. The 2021 update differed from previous updates in taking detailed account of correlations among the input data, a step shown to be important in deriving unbiased frequency values and avoiding underestimation of their uncertainties. It also differed in the procedures used to assess input data and to assign uncertainties to the recommended frequency values, with previous practice being adapted to produce a fully consistent output data set consisting of frequency ratio values as well as absolute frequencies. These changes are significant in the context of an anticipated redefinition of the second in terms of an optical transition or transitions, since optical frequency ratio measurements will be critical for verifying the international consistency of optical clocks prior to the redefinition. In the meantime, the reduced uncertainties for optical SRS resulting from this analysis significantly increases the weight that secondary frequency standards based on these transitions can have in the steering of International Atomic Time (TAI).

“…The next step will be to prepare a draft resolution for the 28th meeting of the CGPM (2026), possibly addressing the necessary choices and the remaining work, with a robust roadmap, to redefine the second in 2030. A paper has been published [55] in the special focus issue of Metrologia devoted to 'Challenges in Time and Frequency Metrology'.…”

Section: Timementioning

confidence: 99%

News from the BIPM laboratories—2023

Stock,

Tavella,

Gressier

et al. 2024

Self Cite

In order to fulfil its mission to ensure and promote the global comparability of measurements, the BIPM operates laboratories in the fields of physical metrology, time, ionizing radiation and chemistry. These laboratories act as centres for scientific and technical collaboration between Member States providing capabilities for international measurement comparisons on a shared cost basis. They coordinate international comparisons of national measurement standards agreed to be of the highest priority, and they establish and maintain appropriate reference standards for use as the basis of key international comparisons at the highest level and provide selected calibrations from them.In the following sections, we provide highlights of the work the laboratories have undertaken during 2023.