Absolute frequency measurement of a <sup>88</sup>Sr<sup>+</sup> clock by direct comparison to a primary frequency standard
Bibliographic record
Abstract
Abstract We report on a measurement of the absolute frequency of the 88Sr+ clock transition via a direct comparison to our cesium fountain clock, National Research Council Canada (NRC)-FCs2. The measurement yield a value of 444 779 044 095 485.404 ± 0.045 Hz. The corresponding fractional uncertainty of 1.0 × 10 − 16 is, to our knowledge, the lowest so far reported for an absolute frequency measurement. The low uncertainty obtained is primarily a consequence of improvements to NRC-FCs2, specifically a systematic uncertainty of 9.3 × 10 − 17 and a stability of 6.3 × 10 − 14 / τ . The measurement was made over a period of 37 days with 68% uptime, for a total measurement time of 2.16 × 10 6 s. The 88Sr+ frequency was also compared to terrestrial time via a global navigation satellite system (GNSS) link to Universal Coordinated Time, yielding a frequency value of 444 779 044 095 485.406 ± 0.089 Hz, which is in agreement with the direct comparison with NRC-FCs2.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.002 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.008 | 0.002 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".