The BIPM , RIKEN and Shimadzu Corporation have signed a Memorandum of Understanding (MoU) to begin an exploratory collaboration on optical frequency standards (OFS). The signing took place on 12 May 2026 in Kawasaki, Japan.
The MoU establishes a preliminary framework to enable discussions and joint studies on the potential role of transportable optical frequency standards in international time and frequency metrology.
Work towards a possible future redefinition of the second requires reliable comparisons between optical frequency standards (OFS). A key requirement identified by the Consultative Committee for Time and Frequency ( CCTF ) is the ability to compare independent realizations of the second at the level of 10⁻¹⁸ and to achieve consistent contribution to Coordinated Universal Time ( UTC ).
Transportable OFS are one approach under consideration for supporting such comparisons. Evaluating their feasibility and conducting technical studies related to operational and environmental requirements, is an important step in the broader roadmap towards the redefinition of the second.
Read the Metrologia paper on the ‘Roadmap towards the redefinition of the second’
The collaboration is expected to involve the National Metrology Institute of Japan (NMIJ), alongside the BIPM, RIKEN and the Shimadzu Corporation, and to remain open, under equal conditions, to other national metrology institutes and partner organizations with a reasonable interest.
Background
Optical frequency standards, including optical lattice clocks and single-ion optical clocks, are based on optical transitions in atoms or ions and offer higher stability and accuracy than current microwave standards used to realize the second. Ensuring their global comparability is a key requirement for any future evolution of the definition of the SI unit of time.