Tsinghua-led team develops nuclear optical clock, Nature publishes results

Tsinghua University and multiple domestic research teams said they developed the world’s first “nuclear optical clock,” advancing quantum precision measurement from electron transitions to atomic nucleus transitions, according to China News Service and CLS. Xinhua also reported the development under the headline “Moving toward more precise timekeeping: Chinese scientists successfully develop nuclear optical clock.” The research results were published in the international journal Nature on Oct 7, the reports said. [ 1 , 2 , 3 ]

The Tsinghua team spent nearly five years on the project and originally developed a 148-nanometer continuous-wave vacuum ultraviolet laser technology, China News Service reported. The team used this light source to precisely drive the nuclear transition of the radioactive isotope thorium-229 and stabilized the laser frequency on that nuclear transition, thereby developing the clock. [ 3 ]

Ding Shiqian, an associate professor in Tsinghua University’s physics department and an adjunct researcher at the Beijing Academy of Quantum Information Sciences, explained the principle. He said an old pendulum swings about once per second, and counting the swings tells time. The nuclear optical clock uses the rhythm of the atomic nucleus as a “pendulum,” with a rhythm of about 2,000 trillion times per second, cutting time very finely, he said. [ 3 ]

According to China News Service, the nuclear optical clock is seen as a new-generation time-frequency standard after atomic microwave clocks and atomic optical clocks. Currently, the most precise atomic optical clocks record the rhythm of electron transitions inside atoms, but achieving extremely high precision requires fine control of electric fields, magnetic fields, temperature and laser system disturbances. As a result, the highest-performance atomic optical clocks still mainly operate in laboratories, and their miniaturization and engineering remain challenging, the report said. The nuclear clock instead shifts the timekeeping reference from electron transitions to the nuclear transition inside thorium-229. [ 3 ]

Ding said the atomic nucleus is only about one part in tens of thousands of the size of the electron cloud surrounding it, which makes the nucleus’s rhythm more stable and the resulting clock potentially more precise. He added that the clock could be miniaturized, allowing a highly precise timing device to be put to practical use rather than remaining a laboratory tool. [ 3 ]

The nuclear optical clock is expected to be applied in navigation and deep space exploration, providing more precise positioning and distance measurement for satellites and spacecraft and serving national major needs, CLS and China News Service reported. [ 2 , 3 ]