近日，美国科罗拉多大学Jun Ye团队研究了固体钍-229核时钟的频率再现性。该研究于2026年1月28日发表在《自然》杂志上。

固态钍-229（²²⁹Th）核钟将为精密计量学与基础物理学研究开辟新路径。利用核跃迁对环境影响的固有低敏感性，固态晶体中可容纳的辐射源数量比当前光晶格原子钟高出数个数量级。此外，仅需简单温控的固态系统是开发可部署紧凑型核钟的关键。

研究组系统探究并表征了²²⁹Th:CaF₂核钟跃迁的频率复现性——这是衡量所有时钟性能的核心指标。他们测量了跃迁线宽与中心频率随掺杂浓度、温度和时间的变化规律。首次报道了受限于晶体本征特性的核跃迁浓度依赖性非均匀线宽，确定²²⁹Th:CaF₂核钟在196(5) K温度下具有最优工作点，此时一阶热灵敏度趋近于零。

该特性使得利用不同四极分裂谱线进行原位温度共感测量成为可能，从而将温度引起的系统频移控制在10^-18量级以下。在195 K温度条件下，两种不同掺杂浓度的²²⁹Th:CaF₂晶体在超过7个月周期内，核跃迁频率复现性达到220 Hz（相对精度1.1×10^-13）。这些成果为理解、调控和利用固态基质中²²⁹Th的相干核激发奠定了基石，并为核钟在约束基本常数随时间变化等前沿应用提供了关键支撑。

附：英文原文

Title: Frequency reproducibility of solid-state thorium-229 nuclear clocks

Author: Ooi, Tian, Doyle, Jack F., Zhang, Chuankun, Higgins, Jacob S., Ye, Jun, Beeks, Kjeld, Sikorsky, Tomas, Schumm, Thorsten

Issue&Volume: 2026-01-28

Abstract: Solid-state thorium-229 (229Th) nuclear clocks1,2,3,4,5 are set to provide new opportunities for precision metrology and fundamental physics6,7,8. Taking advantage of inherent low sensitivity of a nuclear transition to its environment9, orders of magnitude more emitters can be hosted in a solid-state crystal compared with current optical lattice atomic clocks10. Furthermore, solid-state systems needing only simple thermal control11 are key to the development of field-deployable compact clocks. Here we explore and characterize the frequency reproducibility of the 229Th:CaF2 nuclear clock transition, a key performance metric for all clocks. We measure the transition linewidth and centre frequency as a function of the doping concentration, temperature and time. We report the concentration-dependent inhomogeneous linewidth of the nuclear transition, limited by the intrinsic host crystal12 properties. We determine an optimal working temperature for the 229Th:CaF2 nuclear clock at 196(5)K, at which the first-order thermal sensitivity vanishes. This would enable in situ temperature co-sensing using different quadrupole-split lines, reducing the temperature-induced systematic shift below the 1018 fractional frequency uncertainty level. At 195K, the reproducibility of the nuclear transition frequency is 220Hz (fractionally 1.1 × 1013) for two differently doped 229Th:CaF2 crystals over 7months. These results form the foundation for understanding, controlling and harnessing the coherent nuclear excitation of 229Th in solid-state hosts and for their applications in constraining temporal variations of fundamental constants.

DOI: 10.1038/s41586-025-09999-5

Source: https://www.nature.com/articles/s41586-025-09999-5