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Paper in journal Nature Physics is featured as one of the editors’ favourites from the journal’s 15- year lifetime

A peer-reviewed paper entitled Geodesy and metrology with a transportable optical clock describing the work of completed European Metrology Research programme (EMRP) project International timescales with optical clocks (SIB55, ITOC) has been featured by Nature Physics journal as one of their favourites from the last 15 years. The paper is one of the top 1% (based on its Altmetric score) of tracked articles of a similar age in all journals, and has already been cited over 130 times since 2018.

In an article in the October 2020 issue entitled 15 years of Nature Physics, the journal editors look back at their favourite papers from the 15 year lifetime of the journal.

The EMRP project

The International System of Units (SI) unit of time, the second, underpins international timekeeping and is relied upon by power grids, the internet, financial transactions and navigation systems. Improving the accuracy and stability of international timescales will bring more precision to many applications.

The second is currently determined by comparing a microwave source to a fundamental property - an absorption frequency of caesium atoms. However, a new generation of optical clocks, using higher frequency laser light, can now achieve greater accuracy and stability. For any future redefinition of the SI second based on optical clocks, the accuracy of different types of clock must be confirmed by a coordinated programme of comparisons, and their frequencies robustly linked to existing caesium standards.

This project tackled these and other important considerations for a redefinition of the second using optical clocks.

Robust procedures, developed by this project, for analysing the self-consistency of clock comparison data and deriving optimised values for the frequencies of the optical clocks is allowing them to be integrated into international timescales, improving their stability. The work will also enable better informed decisions to be taken on any future redefinition of the second.

The international scientific community will also benefit from validated optical clock performance when conducting tests of fundamental physical theories. Early beneficiaries will include the European Space Agency (ESA) and the European Very Long Baseline Interferometry Network (EVN), who have facilities requiring accurate time and frequency signals. Measurements of gravity potential differences using optical clocks will be important in geodesy, for example, in monitoring the effects of climate change on sea levels.

Project coordinator Helen Margolis from NPL said

‘The recent feature article provided a rare insight into the debates that take place within the Nature Physics editorial office. For our paper, the key question they grappled with was where to draw the line between physics and engineering, but in the end their desire to represent physics when put to practical use tipped the balance in our favour. Publication in Nature Physics has really helped us bring the important work performed within the ITOC project to the attention of a wide audience’.

This EMRP joint research project is part of EURAMET’s European Metrology Research Programme. The EMRP is jointly funded by the EMRP participating countries within EURAMET and the European Union.

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