Steps towards a ²²⁹Th ionic nuclear clock in a linear ion trap

Owing to the presence of a low-energy, long-lived nuclear isomeric state, ²²⁹Th is an ideal candidate for developing the next generation clock — the nuclear clock — holding great promise for both applied and fundamental physics. The ²²⁹Th ionic nuclear optical clock has garnered considerable attention, attributed to its high precision with a relative uncertainty of ≤ 1.5 × 10⁻¹ and the potential for common-mode noise cancellation via self-comparison between the nuclear transition and the electronic transition of thorium ions. In this article, we focus on Thⁿ⁺ ions (n = 1, 2, 3) and present a comprehensive review of the current progress in the development of ionic nuclear clocks, covering essential steps such as ion generation, trapping, and cooling. Furthermore, we discuss the realization of a closed-loop clock cycle, addressing key aspects including stable isomer excitation and efficient isomer deexcitation.