China News Service, Beijing, October 8 (Reporter Ma Shuaisha) Recently, the team of Ding Shiqian, associate professor of Tsinghua University, successfully developed a thorium-229 nuclear optical clock and became the first in the world to implement it. On the evening of October 7, Beijing time, the relevant results paper was published online in the international academic journal Nature.
It is reported that the team used the independently developed 148-nanometer continuous wave vacuum ultraviolet laser and the thorium-229-doped calcium fluoride crystal jointly developed with the cooperative team to achieve thorium-229 nuclear transition absorption spectrum measurement, and stably locked the laser frequency to the nuclear transition to realize nuclear optical clock operation, thus establishing a complete technical system from the core light source, nuclear clock crystal, nuclear transition spectrum to closed-loop operation.
During the development of the nuclear optical clock, Ding Shiqian's team overcame many difficulties. The team developed the 148-nanometer continuous wave vacuum ultraviolet laser for the first time in the world, solving the core light source problem of accurately driving the nuclear transition of thorium-229. With the collaborative research of multiple parties, the team carried out the development of small-volume crystals doped with trace amounts of thorium-229, and successfully grew millimeter-scale high-quality thorium-doped calcium fluoride crystals in one go using only 1.4 micrograms of thorium-229 at the time, meeting the development needs of nuclear optical clocks with very few nuclide resources.
In an interview, Ding Shiqian pointed out that nuclear optical clocks are expected to become a new generation of time and frequency standards after atomic microwave clocks and atomic optical clocks, and are an important frontier in the current field of quantum precision measurement.
He said that currently, atomic optical clocks and atomic microwave clocks use electronic transitions in atoms to provide the most accurate and practical time measurement respectively. Nuclear optical clocks use the internal transition of the thorium-229 atomic nucleus as a frequency reference. Since the scale of atomic nuclei is much smaller than that of atoms, nuclear transitions are less affected by disturbances in the external electromagnetic environment. Therefore, in principle, it is expected to provide a more accurate time and frequency benchmark than atomic optical clocks.
"At the same time, solid-state nuclear optical clocks have potential miniaturization and engineering advantages, and are expected to provide practical technical options for high-precision time and frequency requirements in scenarios such as satellite navigation, deep space exploration, and national defense security," said Ding Shiqian.
Ding Shiqian said that the thorium-229 nuclear transition has significantly enhanced sensitivity to new physical effects such as changes in basic constants, and nuclear optical clocks can provide a new precision detection platform for testing basic physical laws. The realization of nuclear optical clocks also means that the ability of quantum manipulation reaches the scale of atomic nuclei, opening up new research directions for quantum precision measurement and quantum manipulation. (over)
