Scheme for the excitation of thorium-229 nuclei based on electronic bridge excitation

The extremely narrow linewidth of the first nuclear excited state, with an uncertainty of 53 THz, prevents direct laser excitation and realization of the nuclear clock. We present a proposal using the Coulomb crystal of a linear chain formed by 229Th3+ ions, where the nuclei of 229Th3+ ions in the ion trap are excited by the electronic bridge (EB) process.

The 7P1/2 state of the thorium-229 nuclear ground state is chosen for EB excitation. Using the two-level optical Bloch equation under experimental conditions, we calculate that two out of 36 prepared thorium ions in the Coulomb crystal can be excited to the first nuclear excited state, and it takes approximately 2 h to scan over an uncertainty of 0.22 eV. Taking advantage of the transition enhancement of 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.