First optical atomic clock

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Supercharged ions are common substances in the universe, including the sun and other stars. They are so named because they have lost many electrons and hence have a high positive charge. Therefore, the outermost electrons are more strongly bound to the nucleus than neutral or weakly charged atoms.

This makes highly charged ions less sensitive to perturbations from external electromagnetic fields, but more sensitive probes to the fundamental effects of special relativity, quantum electrodynamics, and the atomic nucleus. .

“We therefore hoped that an optical atomic clock with highly charged ions would help us better test these basic theories,” explains PTB physicist Lukas Spieß. This hope has already come true. “He was able to demonstrate quantum electrodynamic nuclear recoil in a five-electron system, an important theoretical prediction that has not been achieved by other experiments to date.”

Previously, the team had to solve some basic problems like detection and cooling after years of work. read. However, creating a very hot plasma creates highly charged ions.

Due to their extreme atomic structure, highly charged ions cannot be directly cooled by laser light or using conventional detection methods. This was resolved through collaboration with his MPIK in Heidelberg and his QUEST institute in his PTB. This was done by isolating a single highly charged argon ion from the hot plasma and storing it in an ion trap along with singly charged beryllium ions.

This allows the indirectly cooling of highly charged ions to be studied using beryllium ions. An advanced cryogenic trap system was then built at MPIK and completed at PTB for subsequent experiments. Some of it was performed by students moving between institutions.

Quantum algorithms developed at PTB then succeeded in further cooling the highly charged ions. This corresponds to a temperature 1/200 millionth of a kelvin above absolute zero. These results will be published in Nature in 2020 and Physical Review X in 2021.

Researchers are now taking the next step. They implemented an optical atomic clock based on argon ions charged 13 times and compared time with the existing ytterbium ion clock at PTB. Doing this required detailed analysis of the system, including understanding the motion of the uploaded ions and the effects of external interfering fields.

They achieved half his measurement uncertainty in 1017. This is comparable to many optical atomic clocks in use today. “We hope that technical improvements will further reduce the uncertainty, which should bring us to the range of the best atomic clocks,” said Pete Schmidt, leader of the research group. I’m here.

Thus, researchers have created serious competition for existing optical atomic clocks based on, for example, individual ytterbium ions or neutral strontium atoms. The methods used are universally applicable and allow the investigation of many different highly charged ions. This includes atomic systems that can be used to search for extensions to the standard model of particle physics.

Other highly charged ions are particularly sensitive to changes in fine structure constants and certain dark matter candidates required by models beyond the standard model, but have not been detected by previous methods.


More information: Lukas Spieß, An optical atomic clock based on a highly charged ion, Nature (2022). DOI: 10.1038/

Journal information: Physical Review X  Nature 

Provided by Physikalisch-Technische Bundesanstalt 

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