The 27th General Conference of Weights and Measures (CGPM) adopted the resolution on the "future redefinition of the second", which aims to redefine the unit of time using optical clocks. It plans to propose a resolution on the redefinition of the second at the 2026 CGPM and adopt a resolution at the 29th CGPM in 2030.
Recently, a research team led by Prof. CHANG Hong and Prof. WU Wenjun from the National Time Service Center of the Chinese Academy of Sciences (NTSC) developed a 87Sr optical clock(NTSC-Sr1). The systematic uncertainty and frequency stability of NTSC-Sr1 are evaluated to be 5.1×10-17 and 6.6×10-16 (τ/s)-0.5, respectively. The absolute frequency of the clock transition is measured with an uncertainty of 4.1×10-16, using the Hydrogen maser to link the International Atomic Time (TAI).
The results were published in Metrologia on Jan. 23.
Researchers presented a new measurement of the absolute frequency of a Sr-87 optical lattice clock, making a link to primary frequency standards through the international atomic time scale. "These measurements are important ahead of the redefinition of the SI second in order to build confidence in the performance of optical frequency standards around the world," said a reviewer of Metrologia.
According to Prof. CHANG Hong, the research team will make NTSC-Sr1 to participate in the calculation of TAI in order to cope with the change of the international definition of "second" and ensure the independence, safety and reliability of China's time standard.
National Time Service Center, Chinese Academy of Sciences