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An optical clock for end-users

Single-ion clock demonstrates robust operation

PTB-News 2.2022
Especially interesting for

astronomic observatories

telecommunications network operators

time laboratories

Due to their higher reference frequency, optical clocks enable measurements that are even more accurate than those of conventional atomic clocks. Until now, however, optical clocks could only be operated by experts in special laboratories. Within the scope of Opticlock, an industry-led pilot project for quantum technologies, a demonstrator of an optical clock has been built. This demonstrator makes the advantages of modern quantum technologies available to end-users in the form of a user- friendly device.

Demonstrator of an optical clock for end-users. The cabinet on the left contains control hardware and electronics. The cabinet on the right-hand side accommodates all lasers and optical setups as well as a wavelength measuring instrument and the ion trap.

In optical clocks, transitions of trapped atoms or ions are driven by laser radiation. During operation, the frequency of the clock laser is tuned to exactly match the resonance frequency and can then be counted as the clock’s beat. This frequency is about 100 000 times higher than the microwave frequency used to define the second, the SI base unit of time. Optical atomic clocks have been investigated in many specialized laboratories around the world to demonstrate the improvements attained due to the considerably higher frequency of optical laser radiation. However, it was previously not possible to operate such systems continuously over a longer period of time or to make them utilizable for operators who did not have a profound knowledge of the clocks’ design. Such optical clocks could be particularly interesting for astronomic observatories and telecommunications network operators who have high system time stability requirements.

Within the scope of a pilot project on quantum technologies funded by the German Federal Ministry of Education and Research (BMBF), six companies, two universities and two research institutes, including PTB, pooled their expertise. Within three years, they succeeded in building an atomic clock demonstrator that is accommodated in two 19ʹʹ server rack cabinets. A reference transition of a single ytterbium ion stored in a radiofrequency ion trap defines the clock rate. All sub-components were optimized for the setup to exhibit best possible reliability and thus ensure robust operation. Several optimization and adjustment routines, which previously had to be made by scientific staff in the lab, have been automated. This not only reduces the demands placed on users of such a clock. The much faster execution minimizes the intervals in which the optical clock does not operate with the highest accuracy.

In a two-week measurement campaign, the optical clock demonstrated its ability to run robustly in continuous operation. Its atomic reference was exploited for 99.8 % of its total operating time. In the remaining time, automatic routines were performed to ensure maximum accuracy. There were no unwanted interruptions of operation and no malfunctions. The estimated timing error after two weeks was smaller than 15 picoseconds. Opticlock thus outperforms commercially available atomic clocks by a factor of 10. The system is to be made available for measurements on operators’ sites and to contribute to the international atomic time scale at PTB.


Nils Huntemann
Department 4.4
Time and Frequency
Phone: +49 531 592-4430
Opens local program for sending emailnils.huntemann(at)ptb.de

Scientific publication

J. Stuhler, M. Abdel Hafiz, B. Arar, A. Bawamia, K. Bergner, M. Biethahn, S. Brakhane, A. Didier, J. Fortágh, M. Halder et al.: Opticlock: Transportable and easy-to-operate optical single-ion clock. Measurement: Sensors 18, 100264 (2021)