High-Accuracy Measurement of the Magnetic Moment Anomaly of the Electron Bound in Hydrogenlike Carbon

We present a new experimental value for the magnetic moment of the electron bound in hydrogenlike carbon (¹²C⁵⁺): gₑₓₚ0ex0ex=0ex0ex2.001041596(5). This is the most precise determination of an atomic gJ factor so far. The experiment was carried out on a single ¹²C⁵⁺ ion stored in a Penning trap. The high accuracy was made possible by spatially separating the induction of spin flips and the analysis of the spin direction. The current theoretical value amounts to gₜₕ0ex0ex=0ex0ex2.001041591(7). Together experiment and theory test the bound-state QED contributions to the gJ factor of a bound electron to a precision of $1%$.