The low-energy, long-lived isomer in ²²⁹Th, first studied in the 1970s as an exotic feature in nuclear physics, continues to inspire a multidisciplinary community of physicists. It has stimulated innovative ideas and studies that expand the understanding of atomic and nuclear structure of heavy elements and of the interaction of nuclei with bound electrons and coherent light. Using the nuclear resonance frequency, determined by the strong and electromagnetic interactions inside the nucleus, it is possible to build a highly precise nuclear clock that will be fundamentally different from all other atomic clocks based on resonant frequencies of the electron shell. The nuclear clock will open opportunities for highly sensitive tests of fundamental principles of physics, particularly in searches for violations of Einstein’s equivalence principle and for new particles and interactions beyond the standard model. It has been proposed to use the nuclear clock to search for variations of the electromagnetic and strong coupling constants and for dark matter searches. The ²²⁹Th nuclear optical clock still represents a major challenge in view of the tremendous gap of nearly 17 orders of magnitude between the present uncertainty in the nuclear transition frequency (about 0.2eV, corresponding to ∼48THz) and the natural linewidth (in the mHz range). Significant experimental progress has been achieved in recent years, which will be briefly reviewed. Moreover, a research strategy will be outlined to consolidate our present knowledge about essential ^229mTh properties, to determine the nuclear transition frequency with laser spectroscopic precision, realize different types of nuclear clocks and apply them in precision frequency comparisons with optical atomic clocks to test fundamental physics. Two avenues will be discussed: laser-cooled trapped ²²⁹Th ions that allow experiments with complete control on the nucleus–electron interaction and minimal systematic frequency shifts, and Th-doped solids enabling experiments at high particle number and in different electronic environments.

^{229 中}的低能量、长寿命异构体Th 于 1970 年代首次作为核物理学的一个奇特特征进行研究，它继续激励着一个多学科的物理学家社区。它激发了创新思想和研究，扩大了对重元素的原子和核结构以及核与束缚电子和相干光相互作用的理解。使用由核内强相互作用和电磁相互作用决定的核共振频率，可以构建一个高度精确的核钟，该钟与基于电子壳共振频率的所有其他原子钟有着根本的不同。核钟将为物理学基本原理的高灵敏度测试提供机会，特别是在寻找违反爱因斯坦等效原理的情况以及超出标准模型的新粒子和相互作用方面。已经提出使用核钟来搜索电磁和强耦合常数的变化以及暗物质搜索。这鉴于目前核跃迁频率（约 0.2eV，对应于~48THz）和自然线宽（在 mHz 范围内）的不确定性之间存在近 17 个数量级的巨大差距，²²⁹ Th 核光学时钟仍然是一项重大挑战）。近年来取得了重大的实验进展，将简要回顾。此外，将概述一项研究策略，以巩固我们目前关于^229m Th基本特性的知识，用激光光谱精度确定核跃迁频率，实现不同类型的核时钟，并将它们应用在与光学原子钟的精密频率比较中，以测试基本的物理。将讨论两种途径： 激光冷却被困²²⁹Th 离子允许实验完全控制核-电子相互作用和最小的系统频移，而 Th 掺杂的固体允许在高粒子数和不同电子环境中进行实验。