Radiative decay of 229mTh in solid-state nuclear clocks

doi:10.1088/1674-1056/ae3e72

Abstract The $^{229}$Th isotope hosts an exceptionally low-energy nuclear transition in the vacuum ultraviolet range, making it a leading candidate for nuclear optical clocks. Recent laser excitation and fluorescence measurements in Th-doped crystals have demonstrated the feasibility of such clocks, yet the precise lifetime of the nuclear excited state remains uncertain. In this work, we build upon the well-established $n^3$ scaling of $M1$ nuclear decay rates, which describes how the radiative decay of a magnetic-dipole transition is modified by the refractive index $n$ of an isotropic and homogeneous medium. Our contribution unifies previously disparate experimental results on $^{229}$Th-doped crystals within a single theoretical framework and delineates the conditions under which the scaling remains valid. We further analyze the limitations of extracting vacuum lifetimes from existing solid-state measurements, highlighting the roles of non-radiative decay channels as well as surface and defect-induced effects, which can invalidate the simple $n^3$ rule under realistic experimental conditions. These insights open new possibilities for reducing interrogation times and improving the overall performance of nuclear clocks.

Keywords: nuclear optical clock thorium-229 quantum optics in dielectric

Received: 27 October 2025
Revised: 07 January 2026
Accepted manuscript online: 28 January 2026

PACS:	42.50.-p	(Quantum optics)
	76.80.+y	(M?ssbauer effect; other γ-ray spectroscopy)
	33.45.+x	(M?ssbauer spectra)

Fund: Project supported by the National Natural Science Foundation of China (Grant Nos. 12474484, U2330401, and 12088101).

Corresponding Authors: Yong Li
E-mail: xwang@gscaep.ac.cn

Cite this article:

Zong-Heng Li(李宗珩) and Xu Wang(王旭) Radiative decay of ^229mTh in solid-state nuclear clocks 2026 Chin. Phys. B 35 064202

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Radiative decay of ^229mTh in solid-state nuclear clocks