The impact of this work is predominantly on the scientific community and on the long-term development of metrological capabilities at the frontiers of measurement science. Longer-term economic impact from knowledge transfer to industry is foreseeable.

After start of the project, a website has been set up to inform about this project. The significant impact on scientific communities is well indicated by 14 conference presentations from partners of the project within the first 9 months, including invited talks at the Joint Conference of the European Frequency and Time Forum and IEEE International Frequency Control Symposium (EFTF/IFCS) and the European Conference on Trapped Ions 2021. A training course on “Optical atomic clocks: basic principles and applications” at the WACQT Summer School 2021 provided ideas to more than 50 participants. A much larger audience has been reached by an online video presentation on YouTube with contributions from project partners has presently more than 150,000 views.

Impact on industrial and other user communities
Optical clocks are attracting much interest in different sectors, such as space, aerospace, telecommunications, and energy networks because of their superior performance compared with established microwave clocks. Key subsystems of optical clocks (e.g. laser systems, reference resonators, frequency combs, ion traps and optical traps) are already commercially available from several vendors. First demonstrators of future commercial clocks, for application beyond fundamental research, are developed directly by or with strong participation of industrial partners within various projects supported by quantum technology initiatives. Sub components of these demonstrators extend to other applications such as precision spectroscopy and quantum information processing. Several project partners have strong links with European and national programmes that aim to develop optical clocks for applications beyond fundamental research. This project will strengthen and widen the relations between NMIs, academic institutes and industry through knowledge exchange and cooperation. For instance, an external collaborator will apply the methodologies on composite clocks developed in the project to the case of transportable clocks or future industrial clocks that do not use highest grade lasers. Moreover, industrial development of optical and electronic systems is supported by the participating NMIs via guidance on target specifications for novel applications and ad-hoc support in the characterisation of commercial prototypes.

Impact on the metrology and scientific communities
This project will improve the level of uncertainty realisable with optical atomic clocks by enabling systems that combine advantages of clocks based on transitions in different species. This will improve the stability achievable with single or few-atom systems and reduce the averaging time required to obtain a targeted statistical uncertainty. Techniques investigated will permit application of new reference systems, including a nuclear transition, that are promising candidates for optical clocks. This will provide input to the selection of suitable reference systems for a redefinition of the SI second, an essential contribution to fundamental metrology and to the long-term development of the SI system of units.

This project will foster new interdisciplinary links, and lead to an exchange of technology and know-how between high-precision optical frequency metrology and nuclear physics. High precision methods for optical frequency standards that have been developed by NMIs will be made available to a wider class of systems of scientific interest, such as highly charged ions. This will contribute to an improved understanding of the structure of atoms, molecules, and nuclei, and to tests of fundamental physics through precision spectroscopic studies and frequency measurements on selected systems of high sensitivity (e.g. for violations of Einstein’s equivalence principle).

This project will develop and strengthen the high-level metrological infrastructure in the measurement of time and frequency, and in the longer term it will improve the capabilities in time scale generation and time dissemination. The consortium will liaise with the time section of BIPM, and will report to the Consultative Committee for Time and Frequency (CCTF), to the Consultative Committee for Length - Consultative Committee for Time and Frequency (CCL-CCTF) Working Group on Frequency Standards (WGPSFS) and to the EURAMET Technical Committee for Time and Frequency (TC-TF). In addition, the results will be reported to the European Metrology Network for Quantum Technologies (EMN-Q), in particular to the section on quantum clocks and atomic sensors, and feedback will be collected.

Impact on relevant standards
The research in this project is fundamental in nature. As such, no standards are possible at present, however relevant quantum standards development organisations will be sought out and informed of project progress as technologies mature over the project’s lifetime.

Longer-term economic, social and environmental impacts
Long-term impact of this research will result from the pivotal role of atomic clocks in the revised SI and in several growing technology sectors. The results will allow the international metrological community to make better informed decisions towards a future redefinition of the SI second. Improved atomic clocks have relevance for technological applications, in sectors such as navigation, space, aerospace, telecommunications and energy networks. Trapped ion optical frequency standards offer excellent accuracy and have the best potential for miniaturisation of the “physics package” (i.e. ion trap, vacuum systems, and optical setup for cooling and detection) and the cooling lasers which is of major importance in their development as payloads on board satellites and aerospace vehicles. Improved optical clocks also allow for geodesy with cm-level precision and applications in geodynamic and climate research.