${}^{225}\mathrm{Ra}^{+}$ ions (nuclear spin $I=1/2$) have transitions that are first-order insensitive to magnetic field noise, which is advantageous for optical clocks and quantum information science. We report on laser cooling and trapping of ${}^{225}\mathrm{Ra}^{+}$ ions and hyperfine splitting measurements of the ion's $7\mathrm{s}{}^2{\mathrm{S}}_{1/2}$, $7\mathrm{p}{}^2{\mathrm{P}}_{1/2}$, and $6\mathrm{d}{}^2{\mathrm{D}}_{3/2}$ states. We measured the ground-state hyperfine constant, $A\left({\mathrm{S}}_{1/2}\right)=$ $-27.684511052\left(5\right)\mathrm{GHz}$, and the quadratic Zeeman coefficient, $C_2=142.3\left(1.0\right)$ $\mathrm{Hz}{\mathrm{G}}^{-2}$, of the ${}^2{\mathrm{S}}_{1/2}(F=0,m_F=0)\leftrightarrow {}^2{\mathrm{S}}_{1/2}(F=1,m_F=0)$ transition. Our result addresses a discrepancy in the literature for the ground-state hyperfine splitting. We measured the hyperfine constants of the ${}^2{\mathrm{P}}_{1/2}$ state, $A\left({\mathrm{P}}_{1/2}\right)=$ $-5.447\left(4\right)\mathrm{GHz}$, and the ${}^2{\mathrm{D}}_{3/2}$ state, $A\left({\mathrm{D}}_{3/2}\right)=$ $-619.7\left(1.1\right)\mathrm{MHz}$. We also performed state preparation and measurement using the ground-state hyperfine levels and realized a fidelity of $0.9951\left(9\right)$.

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• Cooling & trapping
• Laser spectroscopy
• Microwave techniques