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European Frequency and Time Forum

A microwave frequency standard based on the laser cooled 113Cd+ ions

Jianwei Zhang, Z.B. Wang, Shiguang Wang, K. Miao, L.J. Wang

Published Apr 1, 2012• 0 citations
Publisher

Abstract

Trapped ions are applied to the precision frequency metrology thanks to the long interaction time between ions and radiation field. In the past decades, many groups in the world have built microwave or optical frequency standards based on different trapped ions and achieved great improvements. In this article, a microwave frequency standard developed at JMI is reported, which is based on the laser cooled113Cd+ions.

DOI
10.1109/eftf.2012.6502418

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Trapped ions are applied to the precision frequency metrology thanks to the long interaction time between ions and radiation field. In the past decades, many groups in the world have built microwave or optical frequency standards based on different trapped ions and achieved great improvements. In this article, a microwave frequency standard developed at JMI is reported, which is based on the laser cooled113Cd+ions.
Microwave frequency standards based on ions are promising as the next generation atomic clocks. This paper reports the recent progresses of the microwave frequency standard based on laser-cooled113Cd+ions developed at Tsinghua University. Based on the current experimental setup, the ground-state hyperfine splitting of113Cd+is measured with higher precision and a better short-term frequency stability is obtained than before. To improve the performance of the Cd+clock further, a new experimental setup with dual-traps is designed, and bi-ions operation is proposed.
The stability and accuracy of atomic microwave frequency standards (atomic clocks) have been improving at a rate exceeding one order of magnitude per decade for the past 30 years. This sustained improvement has been driven mainly by the many and diverse technological applications requiring highly stable and accurate time and frequency standards. There is no reason to suspect that this rate of progress is slowing. Over the last decade, research and development in atomic frequency standards has tended increasingly towards the use of atom and ion trapping technologies to approach the supposedly ideal unperturbed atomic frequency reference consisting of a single atom or ion either motionless or in free-fall in a perfect, field-free vacuum. This work has been facilitated by the relatively recent development of techniques whereby laser light is used to cool, confine and manipulate atoms or ions. This paper reviews the current status of atomic microwave frequency standards based on trapped atoms and trapped ions, and attempts to explain the motivation for their development and the principles of their operation, with particular emphasis on the physics of factors which limit their performance.
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.