Towards a g-factor determination of the electron bound in highly charged, medium-heavy ions
Birgit Schabinger (Universität Mainz)

Bound-state quantum electrodynamic (BS-QED) calculations can be tested by high-precision measurements of the magnetic moment of the electron bound in hydrogen-like and lithium-like ions. In the past, g-factor measurements were done on hydrogen-like carbon (Z=6) and oxygen (Z=8). A relative experimental uncertainty as low as 5*10-10 has been achieved.
Since the influence of the BS-QED increases with the nuclear charge, experiments with medium-heavy ions are of particular interest. In the current experiment we plan to measure the g-factor of lithium-like and hydrogen-like silicon (Z=14) and calcium (Z=20) ions, respectively. The aim is to reach a relative uncertainty δg/g in the order of 10-9. The g-factor measurement on a single ion will be performed in a double Penning-trap setup via the precise measurement of its cyclotron and spin precession frequency. The first one is obtained by measuring all three eigenfrequencies of the ion in the so-called precision trap and using the invariance theorem. The axial frequency can be measured directly using a tank circuit. In contrast the magnetron and the cyclotron frequency are measured by sideband coupling. The spin precession frequency can be determined by measuring the spin flip probability for different excitation frequencies. Therefore, the trapped ion is irradiated with microwaves at a frequency close to the Larmor frequency and the spin state before and after irradiation is observed. To this end, in the analysis trap an inhomogeneous magnetic field is used to generate a small difference in the axial frequency for the two spin directions. To reach the precision aimed for, the experiment is operated in a closed system at 4.2 K to reduce the electronic noise of the newly developed low-noise detection electronics and to reach storage times of several weeks of the highly charged ions created in-trap by a mini-electron beam ion source. Commissioning experiments on single ions will be presented.