Optical standards and the second's definition
Research context
theory comparison · conditional · As of 2026-10-10
Optical transition standards on the CIPM list are secondary representations of the second; their improved instrument performance does not itself change the SI definition.
Key knowledge
Optical transition standards on the CIPM list are secondary representations of the second; their improved instrument performance does not itself change the SI definition. As checked 10 October 2026, the BIPM roadmap describes a conditional 2030 decision and competing single-transition versus weighted-optical-frequency options, contingent on criteria and consensus.
Conditions and scope
- The existing caesium definition remains the reference until an adopted change takes effect. A recommended optical frequency has uncertainty, unlike a fixed defining constant.
- Clock realization includes environmental/systematic shifts, transfer links and gravitational potential; spectroscopy precision alone does not establish traceability.
Sources · 3
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Bureau International des Poids et Mesures (BIPM)2 sources
- Atomic clock frequency ratios with fractional uncertainty ≤3.2×10⁻¹⁸Alexander Aeppli and BACON/NIST/JILA collaboratorsResearch paper
Evidence and review
Inspected current official secondary-representation list; reviewed 2026-10-10; source check dated 2026-10-10. Scope is limited to the cited statements, equations and assumptions, not the whole publication. Inspected 2030 conditional decision milestone and alternative definition options; reviewed 2026-10-10; source check dated 2026-10-10. Scope is limited to the cited statements, equations and assumptions, not the whole publication. Inspected v2 submitted 16 July 2026: abstract, measurement model, results, discrepancy discussion and systematic checks; initial preprint24 December 2025 and NIST2026 posting are separate dates; source check dated 2026-10-10. Scope is limited to the cited statements, equations and assumptions, not the whole publication.
2026-10-10 · Author source inspection of the displayed claim, model assumptions and equations; independent exact-content and branch-inventory review is a separate gate. Contemporary status is a dated snapshot, not a promise of ongoing monitoring.
Entry details
Permanent link to this entry ↗- Record identity
- research-measurement-optical-second-status
- Revision
- research.1
- Structured reference record
- Postgraduate & research reference