新未名空间

近日，中国科学技术大学潘建伟团队与上海技物所、新疆天文台等单位合作，首次在国际上实现百公里级的自由空间高精度时间频率传递实验，实验结果有望对暗物质探测、物理学基本常数检验、相对论检验等基础物理学研究产生重要影响。该成果于北京时间10月5日晚在国际学术期刊《自然》杂志发表。

Free-space dissemination of time and frequency with 10−19 instability over 113 km

Networks of optical clocks find applications in precise navigation1,2, in efforts to redefine the fundamental unit of the ‘second’3,4,5,6 and in gravitational tests7. As the frequency instability for state-of-the-art optical clocks has reached the 10−19 level8,9, the vision of a global-scale optical network that achieves comparable performances requires the dissemination of time and frequency over a long-distance free-space link with a similar instability of 10−19. However, previous attempts at free-space dissemination of time and frequency at high precision did not extend beyond dozens of kilometres10,11. Here we report time–frequency dissemination with an offset of 6.3 × 10−20 ± 3.4 × 10−19 and an instability of less than 4 × 10−19 at 10,000 s through a free-space link of 113 km. Key technologies essential to this achievement include the deployment of high-power frequency combs, high-stability and high-efficiency optical transceiver systems and efficient linear optical sampling. We observe that the stability we have reached is retained for channel losses up to 89 dB. The technique we report can not only be directly used in ground-based applications, but could also lay the groundwork for future satellite time–frequency dissemination.

https://www.nature.com/articles/s41586-022-05228-5

The time is one of the seven basic units of the International System of Units (SI). Since April 2020, five other basic units have also been relying on the unit of time and frequency because of the precision and stability it can achieve3. Indeed, state-of-the-art optical clocks have demonstrated the most accurate frequency reference, up to a local level of 10−19(refs. 8,9). To remotely access the reference optical clocks and establish a global-scale network, it is also necessary to disseminate time–frequency over long distances with an accuracy of a similar level of 10−19. It is expected that an optical clock network connected by dissemination technology will open up the possibility of many exciting applications, including the next-generation definition of the unit of the ‘second’, the testing of general relativity7,12,13,14, the probing of the changes of physical constants15, the search for gravitational waves and dark matter7,12,16, and long-range quantum networks17.