Single-ion optical clocks and the redefinition of time

Currently, cesium clocks are the standard timekeepers, using the frequency of cesium nucleus spins to measure time. However, the last two decades have seen significant improvements in the output precision of optical clocks that use light to measure atomic oscillations, representing a crucial contribution to the future redefinition of time.

Guan et al. show single-ion optical clocks, featuring isotopes like ⁴⁰Ca⁺, benefit from a five orders of magnitude larger transition frequency than cesium clocks.

Formerly, the accuracy of Ca⁺ clocks were mainly limited by blackbody radiation shift due to temperature uncertainty. However, the researchers said this can be minimized by introducing a cryogenic system to reduce the temperature surrounding the ion.

“We have built not only the best ⁴⁰Ca⁺ optical clock, but also one of the best alkali-like-ion based optical clock,” said author Kelin Gao.

⁴⁰Ca⁺ and other single ion optical clocks are simple to set up, easily transported and will consistently behave the same due to isotope invariability. The ⁴⁰Ca⁺ optical clock achieves an ultra-low uncertainty, meaning its timekeeping would be off by one second over the Earth’s lifetime, and is expected to improve one order of magnitude thanks to cooling systems.

The scientists show that ⁴⁰Ca⁺ optical clocks will achieve almost the same precision under laboratory conditions as while being driven long distances in a car trailer. Transportable ⁴⁰Ca⁺ optical clocks that maintain accurate and stable timekeeping represent a new approach to the construction of world-wide clock networks and the reference of time or frequency in the future.

“These improvements are significant and innovative, and can be applied in different fields, for example, the atomic frequency standard, quantum information and precision measurement,” Gao said.

Source: “⁴⁰Ca⁺ optical clocks in China,” by Hua Guan, Baolin Zhang, Huaqing Zhang, Yao Huang, Yanmei Hao, Mengyan Zeng, and Kelin Gao, AVS Quantum Science (2021). This article can be accessed at https://doi.org/10.1116/5.0056771 .

This paper is part of the Quantum Sensing and Metrology collection, learn more here .