Compare rates, not clock faces
A NIST-listed study compares the frequencies of optical clocks based on aluminium ions, ytterbium and strontium. A ratio describes one clock’s rate relative to another. The April 2026 publication listing reports very small uncertainties and emphasizes repeated comparisons between laboratories. [1]
- Aluminium / ytterbium
- Aluminium / strontium
- Ytterbium / strontium
A shared reference helps the comparison
The authors used a common optical reference distributed between JILA and NIST over a stabilized fibre connection. Their updated July 2026 manuscript describes improved comparison stability and tests of the transfer network. Those checks help separate clock behavior from errors in the comparison apparatus. [2]
Disagreement is useful evidence
Some ratios differed from the team’s earlier campaign by more than the stated uncertainties would suggest. The manuscript calls for further comparisons to resolve these discrepancies. It discusses progress toward redefining the second; it does not announce that the definition has changed. [2]
Go a little deeper
Optional reading · about 1 more minute
A ratio is not a vote
Hypothetical example: Three metronomes produce three pairwise comparisons. If the two comparisons involving one metronome shift together, that suggests where to investigate. It does not prove that device is wrong: the connections used to compare them also need checking.
Two meanings of a better clock
Our interpretation: A steadier comparison makes small differences easier to see. Understanding why different measurements agree or disagree is a further task. Read a precision claim together with the authors’ account of repeatability.
Original sources
Attributed synthesis, not original reporting. Examples labeled hypothetical or illustrative are explanatory. Reviewing a source does not independently validate its findings.
- NIST: optical clock frequency ratios ↗
NIST listing dated April 10, 2026; abstract checked September 24. This listing links to a manuscript with a later revision.
- Aeppli and colleagues: atomic clock frequency ratios, version 2 ↗
July 16, 2026 arXiv version; comparison architecture, discrepancy discussion and network analytics read September 24, 2026. No independent replication claimed.