Using the Th III Ion for a Nuclear Clock and Searches for New Physics

TL;DR

This paper explores the Th III ion's electronic structure and its potential for a nuclear clock, demonstrating enhanced nuclear excitation via electronic bridge processes and its usefulness in probing new physics such as axion fields and fundamental constant variations.

Contribution

It introduces a method to significantly enhance nuclear excitation in Th III ion and highlights its applications in precision measurements and fundamental physics tests.

Findings

Electronic bridge process can be enhanced 10,000 times with proper laser tuning.

Electrons reduce the nuclear excited state lifetime by 1.7 times.

Th III ion's level crossing makes transition frequencies highly sensitive to changes in the fine-structure constant.

Abstract

The 229Th nucleus possesses a unique low-frequency transition at 8.4 eV, which is being considered for the development of an extremely accurate nuclear clock. We investigate an electronic bridge process in the Th III ion, where nuclear excitation occurs via electronic transitions, and demonstrate that a proper choice of laser frequencies can lead to 10,000 enhancement of this effect. Electrons also reduce 1.7 times the lifetime of the nuclear excited state. Additionally, the electronic structure of the Th III ion exhibits features that make it particularly useful for probing new physics. Notably, it contains a metastable state connected to the ground state via a weak M2 transition, which can be utilized for quantum information processing, as well as searches for oscillating axion field, violation of local Lorentz invariance, test of the Einstein's equivalence principle, and measurement of nuclear weak quadrupole moment. The electronic states of the ion present a unique case of level crossing involving the 5f, 6d, and 7s single-electron states. This crossing renders the transition frequencies highly sensitive to potential time-variation of the fine-structure constant.