China Becomes First to Achieve Operation of a Thorium-229 Nuclear Optical Clock, Bringing Quantum Precision Measurement into the Atomic Nucleus Scale

Recently, the team of Ding Shiqian, associate professor in the Department of Physics at Tsinghua University, published important results online in the international academic journal Nature, announcing the successful development of a thorium-229 nuclear optical clock and the achievement of its stable operation. This work was completed independently in the same period as that of a European team, making China the first internationally to achieve operation of a thorium-229 nuclear optical clock, marking the successful extension of the time measurement standard from electronic transitions to nuclear transitions.

It is understood that a nuclear optical clock uses the internal transition of the thorium-229 atomic nucleus as a time-frequency reference. Ding Shiqian, one of the corresponding authors of the paper, introduced that the pendulum of an old-fashioned wall clock swings about once per second, whereas a nuclear optical clock uses the beat of the atomic nucleus as its “pendulum,” with a beat frequency of up to about 2 quadrillion times per second. Because the size of the atomic nucleus is only a few tens of thousandths of the electron cloud outside the nucleus, it is less disturbed by the external electromagnetic environment and, in principle, is expected to provide a time-frequency standard of higher precision than traditional atomic optical clocks.

In this research and development work, the co-first authors of the paper included several “post-00s” doctoral students, and the team divided tasks and collaborated to overcome multiple key technical bottlenecks. The Tsinghua University team established a complete technical system, not only achieving the key leap from measuring nuclear transitions to timekeeping with nuclear transitions, but also advancing ultrahigh-precision timekeeping devices from small-volume laboratory tools toward engineering practicality.

It is reported that nuclear optical clocks are expected to become a new-generation time-frequency standard after atomic microwave clocks and atomic optical clocks. Solid-state nuclear optical clocks have the potential advantages of miniaturization and engineering, and in the future are expected to provide practical technical options for high-precision time-frequency needs in scenarios such as satellite navigation and deep space exploration. At the same time, this achievement can also serve as a precision detection platform for testing fundamental physical laws, demonstrating that China has achieved international leadership in the frontier direction of nuclear optical clocks and opening up a new research direction for quantum precision measurement and quantum manipulation.