International optical clock comparison using the European optical fiber network
Year: 2026
Type: article
Abstract: Optical clocks have achieved remarkable estimated fractional frequency uncertainties reaching the 10 − 18 level and below, enabling applications in fundamental physics, general relativity, and geodesy. However, the challenge of verifying the international consistency of optical clocks remains critical as efforts intensify toward redefining the SI second based on an optical transition or transitions. We report on a two-month international clock comparison campaign involving seven optical clocks in four national metrology institutes (INRIM, LNE-OP, NPL, and PTB) connected via the optical fiber network established in Europe. The campaign resulted in optical frequency ratios with uncertainties ranging from 7.7 × 10 − 18 to 6.1 × 10 − 17 . Among the results, the Yb + 171 ( E 3 ) clocks at NPL and PTB demonstrated agreement within an uncertainty of 7.7 × 10 − 18 , marking the first international verification of two independently developed optical clocks below one part in 10 17 . The operation of the Hg 199 clock at LNE-OP (formerly LNE-SYRTE) resulted in frequency ratios with improved uncertainties with Yb + 171 ( E 3 ) , Yb 171 , and Sr 87 optical clocks. These results provide input for the redefinition of the second and underscore how fiber-linked clock networks can advance metrology and scientific applications.
Source: Physical Review Research
DOI: 10.1103/l4bh-ryxs
Authors: Marco Pizzocaro, Clara Zyskind, Anne Amy-Klein, Erik Benkler, Sebastien Bize, Davide Calonico, Etienne Cantin, Christian Chardonnet, Cecilia Clivati, Stefano Condio, E. Anne Curtis, Simone Donadello, Sören Dörscher, Chen-Hao Feng, Melina Filzinger, Jacques-Olivier Gaudron, Rachel M. Godun, Irene Goti, Ian R. Hill, Wei Huang, Nils Huntemann, Matthew Johnson, Joshua Klose, Jochen Kronjäger, Alexander Kuhl, Rodolphe Le Targat, Filippo Levi, Burghard Lipphardt, Christian Lisdat, Jerome Lodewyck, Olivier Lopez, Helen S. Margolis, Maxime Mazouth-Laurol, Alberto Mura, Benjamin Pointard, Paul-Eric Pottie, Matias Risaro, Billy I. Robertson, Marco Schioppo, Kilian Stahl, Martin Steinel, Alexandra Tofful, Mads Tønnes, Jacob Tunesi
Institutions: Istituto Nazionale di Ricerca Metrologica, Centre National de la Recherche Scientifique, Université de Lille, Université Paris Sciences et Lettres, Observatoire de Paris, Sorbonne Université, Laboratoire Temps Espace, Université Sorbonne Paris Nord, Laboratoire de physique des lasers, Physikalisch-Technische Bundesanstalt, Federal Institute For Materials Research and Testing, National Physical Laboratory
Language: English
Subfield: Atomic and Molecular Physics, and Optics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $2,625
OpenAlex ID: W7167799413