A team of researchers from the University of Science and Technology of China (USTC), including Pan Jianwei, Dai Hanning, Chen Yuao, and Peng Chengzhi, have made a significant leap forward in optical clock research. They have successfully enhanced the stability and reduced the uncertainty of a strontium atomic optical lattice clock to the 10⁻¹⁹ level. This translates to an error margin of no more than 1 second over a span of roughly 30 billion years, positioning it among the elite high-precision optical clocks that are poised to redefine the second in the International System of Units (SI). This milestone underscores China’s ascendancy to the forefront of precise time measurement research on the global stage, with their findings published in the esteemed international metrology journal Metrologia on March 5.

As the pinnacle of current time-frequency standards, the essence of an optical clock lies in its utilization of frequency signals generated by atomic internal energy level transitions to meticulously define time, thereby offering unparalleled timing precision. It stands as a direct enabler for the redefinition of the 'second' in the SI, propelling the global time standard into the optical era with an accuracy boost of four orders of magnitude compared to existing microwave time standards. Optical clocks not only furnish a dependable time reference for cutting-edge technologies such as satellite navigation, communication, and precise measurement but also pave the way for novel platforms in fundamental physics research. These include probing general relativity, detecting gravitational waves, and delving into the mysteries of dark matter.

When an optical clock surpasses the 10⁻¹⁹ threshold in both stability and uncertainty, a host of pivotal frontier applications become feasible. These encompass achieving millimeter-level precision in gravity potential and altitude measurements, bolstering disaster prevention and resource exploration efforts, and introducing innovative methods for dark matter detection that may outperform traditional particle experiment platforms. Notably, this level of precision far surpasses the threshold requirements stipulated by the international metrology community for redefining the 'second.' The dual achievement of 10⁻¹⁹ in stability and uncertainty can directly contribute key technologies and position China as a frontrunner in the forthcoming redefinition of the 'second.'

Previously, the combined performance in stability and uncertainty of optical clocks worldwide predominantly hovered at the 10⁻¹⁸ level, with only a select few top-tier institutions nearing or attaining this benchmark. The USTC research team embarked on a long-term, systematic endeavor to tackle key bottlenecks impeding optical clock performance. Their recent accomplishments include multiple breakthroughs in stability and uncertainty, culminating in a comprehensive system uncertainty for the optical clock of 9.2 × 10⁻¹⁹ and laying a robust foundation for the in-depth application of optical clocks across various domains.