Resonance nuclear excitation of the $^{229}$Th nucleus via electronic bridge process in Th~II

TL;DR

This paper explores the electronic bridge process in Th$^+$ ions to enhance nuclear excitation of $^{229}$Th, revealing resonance conditions that could improve nuclear clock precision and affect nuclear state lifetimes.

Contribution

It identifies specific electronic resonances in Th$^+$ ions that significantly enhance nuclear excitation via the electronic bridge process.

Findings

Resonance conditions in Th$^+$ ions can dramatically increase nuclear excitation rates.

Electronic interactions can shorten the lifetime of the nuclear excited state.

Proper laser tuning enables efficient nuclear excitation through electronic transitions.

Abstract

The 8.4 eV transition in the $^{229}$Th nucleus is the basis for a high-precision nuclear clock with exceptional sensitivity to new physics effects. We have identified several cases in the Th$^+$ ion where electronic excitations closely resonate with the nuclear excitation, with the smallest energy difference being $\Delta = -0.09$ cm$^{-1}$. We investigate the electronic bridge process, in which nuclear excitation is induced via electronic transitions, and demonstrate that a proper selection of laser frequencies can lead to a dramatic enhancement of this effect. Additionally, we show that the interaction with electrons significantly shortens the lifetime of the nuclear excited state.