BEIJING, Oct. 8 (Xinhua) -- Chinese scientists have developed a nuclear clock and achieved stable operation, shifting ultra-precise time measurement from electron transitions inside atoms to transitions within atomic nuclei, according to a research article published in the journal Nature.
Solid-state nuclear clocks have potential advantages in miniaturization and engineering, and are expected to meet the high-precision time and frequency requirements in such scenarios as satellite navigation and deep-space exploration.
The nuclear clock uses lasers to drive precise energy-level transitions within the atomic nucleus of thorium-229, a special radioactive isotope, and uses the frequency of these nuclear transitions as its time reference. Researchers built the device with a self-developed 148-nanometer continuous-wave vacuum ultraviolet laser and a thorium-229-doped calcium fluoride crystal.
The new clock is expected to set a next-generation time and frequency standard, and marks an important breakthrough in the field of quantum precision measurement, said Zhai Hui, head of the Department of Physics at Tsinghua University.
"The successful development and stable operation of the nuclear clock means that the capability of quantum manipulation has extended to the nuclear scale," said Zhai.
Atomic clocks use transitions between specific energy levels of electrons inside atoms as their frequency reference, making them the most accurate timekeeping devices available so far. The nuclear clock, however, uses transitions between different nuclear energy levels to measure time.
Since the atomic nucleus scale is far smaller than the atom and nuclear transition can be less sensitive to some external electromagnetic disturbances, nuclear clocks are expected to provide a more precise and more practical time and frequency standard than atomic clocks.
A research team led by Ding Shiqian, associate professor in the Department of Physics at Tsinghua University, developed the world's first 148-nanometer continuous-wave vacuum ultraviolet laser, solving the core light source challenge of precisely driving energy-level transitions inside the thorium-229 atomic nucleus.
In collaboration with partners, they also developed a thorium-229-doped calcium fluoride crystal using only 1.4 micrograms of thorium-229, laying a core technological foundation for the development of the nuclear clock, according to the researchers.
"We have established a complete technological system covering the key light source, nuclear clock crystal, nuclear transition spectrum and closed-loop operation," said Ding. ■
