Excited-state magnetic properties of carbon-like $\text{Ca}^{14+}$
Lukas J. Spieß, Shuying Chen, Alexander Wilzewski, Malte Wehrheim, Jan Gilles, Andrey Surzhykov, Erik Benkler, Melina Filzinger, Martin Steinel, Nils Huntemann, Charles Cheung, Sergey G. Porsev, Andrey I. Bondarev, Marianna S. Safronova, José R. Crespo López-Urrutia, Piet O. Schmidt
Published: 2025/2/26
Abstract
We measured the $g$-factor of the excited state $^3\text{P}_1$ in $\text{Ca}^{14+}$ ion to be $g = 1.499032(6)$ with a relative uncertainty of $4\times10^{-6}$. The magnetic field magnitude is derived from the Zeeman splitting of a $\text{Be}^+$ ion, co-trapped in the same linear Paul trap as the highly charged $\text{Ca}^{14+}$ ion. Furthermore, we experimentally determined the second-order Zeeman coefficient $C_2$ of the $^3\text{P}_0$ - $^3\text{P}_1$ clock transition. For the $m_J=0\rightarrow m_{J'}=0$ transition, we obtain $C_2 = 0.39\pm0.04\text{HzmT}^{-2}$, which is to our knowledge the smallest reported for any atomic transition to date. This confirms the predicted low sensitivity of highly charged ions to higher-order Zeeman effects, making them ideal candidates for high-precision optical clocks. Comparison of the experimental results with our state-of-the art electronic structure calculations shows good agreement, and demonstrates the significance of the frequency-dependent Breit contribution, negative energy states and QED effects on magnetic moments.