近日，美国科罗拉多大学的Jun Ye及其研究小组与美国加州大学的Eric R. Hudson等人合作并取得一项新进展。经过不懈努力，他们研制出用于固态核时钟的四氟化钍-299薄膜。相关研究成果已于2024年12月18日在国际权威学术期刊《自然》上发表。

本研究展示了一种可能具有可扩展性的解决方案，即通过物理气相沉积工艺生长的四氟化钍-299（²⁹⁹ThF?）薄膜中，实现了对钍-229核跃迁的激光激发，且仅消耗了微克量的钍-229材料。

²²⁹ThF₄薄膜与光子学平台和纳米制造工具天然兼容，可与激光源和探测器集成，为开发一种集成式、可现场部署的固态核时钟铺平了道路，其放射性比典型的钍-229掺杂晶体低三个数量级。此外，²²⁹ThF₄中高密度的核发射体，也潜在地为新领域的量子光学研究提供了可能。最后，研究人员评估了基于无缺陷²²⁹ThF₄晶体的核时钟的性能。

据悉，经过近50年的探索，最近已直接用激光激发并高精度光谱测量了，真空紫外波段下的钍-229核同质异能态跃迁。基于这一跃迁的核时钟预计比当前的光学原子钟更稳定，甚至可能超越其性能。这些时钟还有望为超越标准模型的新物理提供灵敏的测试。鉴于这些重要的进展和应用，预计对多个平台上的钍-229光谱靶标的需求将大幅增加。然而，由于钍-229材料的稀缺性和放射性，生长和处理之前测量中使用的高浓度钍-229掺杂晶体具有挑战性。

附：英文原文

Title: ²²⁹ThF₄ thin films for solid-state nuclear clocks

Author: Zhang, Chuankun, von der Wense, Lars, Doyle, Jack F., Higgins, Jacob S., Ooi, Tian, Friebel, Hans U., Ye, Jun, Elwell, R., Terhune, J. E. S., Morgan, H. W. T., Alexandrova, A. N., Tran Tan, H. B., Derevianko, Andrei, Hudson, Eric R.

Issue&Volume: 2024-12-18

Abstract: After nearly 50years of searching, the vacuum ultraviolet ²²⁹Th nuclear isomeric transition has recently been directly laser excited and measured with high spectroscopic precision. Nuclear clocks based on this transition are expected to be more robust than and may outperform current optical atomic clocks. These clocks also promise sensitive tests for new physics beyond the standard model. In light of these important advances and applications, a substantial increase in the need for ²²⁹Th spectroscopy targets in several platforms is anticipated. However, the growth and handling of high-concentration ²²⁹Th-doped crystals used in previous measurements are challenging because of the scarcity and radioactivity of the ²²⁹Th material. Here we demonstrate a potentially scalable solution to these problems by performing laser excitation of the nuclear transition in ²²⁹ThF₄ thin films grown using a physical vapour deposition process, consuming only micrograms of ²²⁹Th material. The ²²⁹ThF₄ thin films are intrinsically compatible with photonics platforms and nanofabrication tools for integration with laser sources and detectors, paving the way for an integrated and field-deployable solid-state nuclear clock with radioactivity up to three orders of magnitude smaller than typical ²²⁹Th-doped crystals. The high nuclear emitter density in ²²⁹ThF₄ also potentially enables quantum optics studies in a new regime. Finally, we present the estimation of the performance of a nuclear clock based on a defect-free ThF₄ crystal.

DOI: 10.1038/s41586-024-08256-5

Source: https://www.nature.com/articles/s41586-024-08256-5