A scheme for excitation of thorium-229 nuclei based on the electronic bridge excitaion

TL;DR

This paper proposes a method using electronic bridge excitation in a Coulomb crystal of Th-229 ions to excite the nuclear state, potentially enabling nuclear clock development despite narrow linewidth challenges.

Contribution

It introduces a novel excitation scheme for Th-229 nuclei using electronic bridge in a Coulomb crystal, improving excitation efficiency and energy uncertainty control.

Findings

2 out of 36 ions can be excited in 2 hours

Energy uncertainty can be reduced to about 1 GHz

The method leverages transition enhancement and crystal stability

Abstract

Thorium-229 possesses the lowest nuclear first excited state with an energy of about 8 eV. The extremely narrow linewidth of the nuclear first excited state with the uncertainty of 53 THz prevents the direct laser excitation and the realization of the nuclear clock. We present a proposal using the Coulomb crystal of a linear chain formed by the $^{229}$Th$^{3+}$ ions, the nuclei of $^{229}$Th$^{3+}$ ions in the ion trap are excited by the electronic bridge (EB) process. The 7$P_{1/2}$ state of the thorium-229 nuclear ground state is chosen for the EB excitation. Using the two-level optical Bloch equation under experimental conditions, we calculate that 2 out of 36 prepared thorium ions in the Coulomb crystal can be excited to the nuclear first excited state, and it takes about 2 hours to scan over the uncertainty of 0.22 eV. Taking the advantage of transition enhancement of the EB and the long stability of the Coulomb crystal, the energy uncertainty of the first excited state can be limited to the order of 1 GHz.