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The first demonstration of an optical clock based on a highly charged ion published in the journal Nature

Since 1967 atomic clocks based on the hyper-fine transitions of the caesium atom have been used to realise the second in the International System of Units (the SI).

These types of time reference standards also underlie the backbone of many everyday technologies that rely on precise time keeping such as banking transactions, telecommunication, and navigation.

Optical clocks now exist, where atoms or ions are ‘trapped’ by lasers, that have a measurement uncertainty two orders of magnitude lower than the best caesium clock. However, to date, no leading candidate for a new primary standard for time has been identified.

EMPIR project Two-species composite atomic clocks (20FUN01, TSCAC) has, for the first ever time, demonstrated an optical clock based upon a highly charged ion (HCI) of an argon atom. This work builds on the achievements of researchers from previous EMRP and EMPIR projects, most recently Coulomb Crystals for Clocks (17FUN07, CC4C) and Robust Optical Clocks for International Timescales (18SIB05, ROCIT).

Optical transitions in highly charged ions have the potential to be more than a million times more accurate than the present state of the art. This could open a range of applications – from improved satellite positioning systems with sub-millimetre accuracy, to new tests for fundamental physics. They could also play a part in a future redefinition of the SI second.

The work of the TSCAC project has presented the first realisation of this new class of clocks. The consortium has demonstrated a systematic frequency uncertainty of 2.2×10−17 for a magnetic-dipole transition in Argon 13+ ions (Ar13+) - which is already comparable to many optical clocks currently in operation.

This significance of this work has been recognised by its publication in an open-access article in the prestigious journal Nature: “An optical atomic clock based on a highly charged ion”. The paper can also be accessed via a physics repository link. The coordinator for this project, and also an author on the Nature article, Nils Huntemann (PTB), Germany’s National Metrology Institute) said about the importance of this work: 

“It demonstrates that technical challenges associated with highly charged ions are manageable and that the extraordinary atomic properties and low sensitivity to external electromagnetic perturbations provide a huge potential for much higher accuracy of future atomic clocks. I am very confident these clocks will be used to provide improved searches for new-physics effects and find application beyond fundamental research in the next few years. Finally, the fact that these highly charged ions also provide reference transitions at very high laser frequencies is a clear advantage over all established systems.”

EMPIR projects are co-funded by the European Union's Horizon 2020 research and innovation programme and the EMPIR Participating States.

EMRP joint research projects are 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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