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  • Open Access

Search for variations of the fine-structure constant via the hyperfine electronic bridge in highly charged Th229 ions

Wu Wang1,2,3, Stephan Fritzsche2,3,4,*, and Yong Li1,†

  • *Contact author: s.fritzsche@gsi.de
  • †Contact author: yongli@hainanu.edu.cn
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Phys. Rev. A 112, 022811 – Published 13 August, 2025

DOI: https://doi.org/10.1103/64n6-9b44

Abstract

The search for variations of the fine-structure constant α by using atomic clocks has driven the development of novel atomic clock technologies. Among these, the Th229 nuclear clock based on nuclear transition stands out due to its high sensitivity. Previous studies on the α variation in atomic clocks have typically focused purely either on a nuclear or electronic transition but not on the hyperfine electronic bridge (HEB) transitions, which involve simultaneous changes in both nuclear and electronic structures. In this work, we propose to search for the α variation by measuring the 3.14-eV HEB transition between the hyperfine levels [Ie,(4f12)Je=4,Fe] and [Ig,(4f12)Je=2,Fg] of Th32+229 ions, and the 2.39-eV HEB transition between [Ie,(4f4)Jg=4,Fe] and [Ig,(4f4)Je=2,Fg] of Th40+229 ions. These two HEB transitions exhibit remarkably large sensitivity factors Kα of about −2.2×104 and −2.9×104, respectively. Compared to the nuclear-clock transition (Ie to Ig) in bare ions, the sensitivity factors are significantly enhanced by factors of 2.7 and 3.5. Moreover, both the 3.14- and 2.39-eV HEB transitions are well supported by current high-precision laser technology, making our approach promising for improving the precision of α variation detection.

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Phys. Rev. A 112, 022811– Published 13 August, 2025
  • Received 21 May 2025
  • Accepted 24 July 2025
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