Excited-State Magnetic Properties of Carbon-like Ca^{14+}

We measured the g-factor of the excited-state ^{3}P_{1} in Ca^{14+} ion to be g=1.499032(6) with a relative uncertainty of 4×10^{-6}. The magnetic field magnitude is derived from the Zeeman splitting of a Be^{+} ion, cotrapped in the same linear Paul trap as the highly charged Ca^{14+} ion. Furthermore, we experimentally determined the second-order Zeeman coefficient C_{2} of the ^{3}P_{0}-^{3}P_{1} clock transition. For the m_{J}=0→m_{J^{'}}=0 transition, we obtained C_{2}=0.39±0.04  Hz mT^{-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.