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Optics Letters

Laser-cooled 171 Yb + microwave clock with a systematic uncertainty of 7.8×10 −15

Yong Chen, Y. Zheng, S. N. Miao, W. X. Shi, S. T. Chen, J. W. Zhang, L. J. Wang

Published Aug 28, 2025• 2 citations
Publisher

Abstract

We present a transportable laser-cooled ion microwave clock based on the ground-state hyperfine splitting of 171 Yb + . The system achieves a systematic uncertainty of 7.8×10 −15 and a short-term frequency stability of 9.5×10 −13 / τ . Enhancements to the magnetic-field system suppress the decoherence process in the multi-body ion ensemble and reduce the second-order Zeeman frequency shift by a factor of two. The absolute microwave frequency is measured to be 12 642 812 118.468 6(3) Hz, consistent with the previous measurements and demonstrating twice the precision of the current state-of-the-art.

DOI
10.1364/ol.570488

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We present a transportable laser-cooled ion microwave clock based on the ground-state hyperfine splitting of 171 Yb + . The system achieves a systematic uncertainty of 7.8×10 −15 and a short-term frequency stability of 9.5×10 −13 / τ . Enhancements to the magnetic-field system suppress the decoherence process in the multi-body ion ensemble and reduce the second-order Zeeman frequency shift by a factor of two. The absolute microwave frequency is measured to be 12 642 812 118.468 6(3) Hz, consistent with the previous measurements and demonstrating twice the precision of the current state-of-the-art.
We report on the development of a microwave frequency standard based on a laser-cooled 171 Y b + ion trap system. The electronics , lasers, and magnetic shields are integrated into a single physical package. With over 105 ions are stably trapped, the system offers a high signal-to-noise ratio Ramsey line-shape. In comparison with previous work, the frequency instability of a 171 Y b + microwave clock was further improved to 8.5 × 10 − 13 / τ for averaging times between 10 and 1000 s. Essential systematic shifts and uncertainties are also estimated.
Abstract As a candidate for the next generation microwave clock, microwave atomic clocks based on trapped ions are currently studied worldwide. Since 2010, our team at Tsinghua University has been committed to developing a high-performance 113Cd+ microwave ion clock. In 2021, the laser-cooled cadmium-ion microwave clock constructed in our laboratory demonstrated remarkable performance, with a short-term instability of 4.2 × 10 − 13 / τ and a relative frequency uncertainty of 1.8 × 10−14, improving nearly three orders of magnitude compared to the result from JPL. The 0-0 ground-state hyperfine splitting frequency of 113Cd+ was determined to be 15199862855.02799(27) Hz, currently the most accurate measurement result for this transition frequency. Apart from that, we introduced the sympathetic cooling technology into the experiment of cadmium-ion microwave clock. Using 40Ca+ as the coolant ion, we obtained Ramsey patterns with a free evolution time of up to 100 seconds, ultimately improving the short-term instability of the system to 3.48 × 10 − 13 / τ . Moreover, a microwave frequency standard based on laser-cooled 171Yb+ ions has also been developed in our laboratory since 2021. The short-term frequency instability was measured to be 8.5 × 10 − 13 / τ . The ground-state hyperfine splitting frequency of 171Yb+ was determined to be 12642812118.4674(8) Hz with a fractional frequency uncertainty of 6.33 × 10−14.
As a candidate for the next generation microwave clock, microwave atomic clocks based on trapped ions are currently studied worldwide. Since 2010, our team at Tsinghua University has been committed to developing a high-performance113Cd+^{113}\text{Cd}^{+}113Cd+microwave ion clock. In 2021, the laser-cooled cadmium-ion microwave clock constructed in our laboratory demonstrated remarkable performance, with a short-term instability of4.2×10−13/τ4.2\times 10^{-13}/\sqrt{\tau}4.2×10−13/τ​and a relative frequency uncertainty of1.8×10−141.8\times 10^{-14}1.8×10−14, improving nearly three orders of magnitude compared to the result from JPL. The ground-state hyperfine splitting of113Cd+^{113}\text{Cd}^{+}113Cd+was determined to be 15199862855.02799(27) Hz, currently the most accurate measurement result for this transition frequency. Apart from that, we introduced the sympathetic cooling technology into the experiment of cadmium-ion microwave clock. Using40Ca+^{40}\text{Ca}^{+}40Ca+as the coolant ion, we obtained Ramsey patterns with a free evolution time of up to 100 seconds, ultimately improving the short-term instability of the system to3.48×10−13/τ3.48\times 10^{-13}/\sqrt{\tau}3.48×10−13/τ​.
A single ion whose energy levels are hyperfine split, 171 Yb + , was electrodynamically trapped and laser cooled. The residual energy of both its driven motion and its secular motion was 11 μeV. Radiofrequency-optical double-resonance excitation yields spectra whose 40 Hz wide lines are determined so far by the duration of the ion's interaction with the 12.6 GHz radiation. These results prove that a microwave clock is feasible with its fractional systematic uncertainty not exceeding 10 −16 .