Progress towards a Radium-225 ion optical clock

Radium-225 has nuclear spin 1/2 and other favorable properties for optical clocks, quantum information science, and tests of fundamental symmetries. With trapped and laser cooled radium ions we have measured the hyperfine splitting of the 7s ²S_1/2 ground state, 7p ²P_1/2 excited state, and the 6d ²D_3/2 excited state. These levels are important for Doppler cooling the ion and for an optical clock that uses only three electronic states. We have driven the ²S_1/2(F = 0, m_F = 0) ↔ ²D_5/2(F = 2, m_F = 0) first-order magnetic field insensitive clock transition as well as the ²D_5/2 (F=2) ↔ ²P_3/2 (F=1) cleanout transition, and are performing spectroscopy of the S_1/2 ↔ D_5/2 transition. We are working towards running a ²²⁵Ra⁺ clock and characterizing systematics.