Optical clocks for the redefinition of the SI second

Project: EU project

Project Details


Bringing European optical clocks to the stage where they regularly contribute to International Atomic Time.

A future redefinition of the second is anticipated as optical atomic clocks have overtaken caesium clocks in terms of fractional frequency instability and estimated systematic uncertainty. However, no optical clock has yet contributed to the TAI.

Project brings optical clocks to the point where they can contribute regularly to the international timescales. This is a prerequisite for redefinition of the second in terms of an optical frequency.

VTT MIKES develops a Sr+ optical clock and contributes to clock comparisons via GPS PPP links.

Call 2018: SI Broader Scope

This project has received funding from the EMPIR programme co-financed by the Participating States and from the European Union’s Horizon 2020 research and innovation programme.
Effective start/end date1/05/1930/04/22

Collaborative partners

  • National Physical Laboratory (NPL) (lead)
  • BA66 National metrology institute VTT MIKES
  • Czech Metrology Institute (CMI) (Project partner)
  • Central Office of Measures (GUM) (Project partner)
  • National Metrological Institute (INRIM) (Project partner)
  • Laboratoire National de Métrologie et d’Essais (LNE) (Project partner)
  • Paris Observatory (Project partner)
  • German National Metrology Institute (PTB) (Project partner)
  • Ben-Gurion University of the Negev (Project partner)
  • French National Center for Scientific Research (CNRS) (Project partner)
  • Leibniz University Hannover (Project partner)
  • Politecnico di Torino (Project partner)
  • Space Research Center of the Polish Academy of Sciences (Project partner)
  • Nicolaus Copernicus University (Project partner)


  • EURAMET e.V.


  • optical clock
  • atomic clock
  • SI second
  • international timescales