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Abstract

The cryogenic double Penning-trap experiment Alphatrap aims to test bound-state quantum electrodynamics (BS-QED) under extreme conditions by measuring the magnetic moment (g-factor) of electrons bound to the nucleus of heavy highly charged ions (HCIs). The bound electron g-factor is measured employing the double-trap technique which uses the continuous Stern-Gerlach effect (CSGE) for a nondestructive detection of the spin state of the ion. The result of this thesis is twofold. In order to improve the achievable precision of future measurements the implementation of sympathetic laser cooling is envisaged. For this purpose a laser system was integrated into the existing setup and laser cooling of ⁹Be⁺ was demonstrated for the first time at Alphatrap. For the axial temperature of a single beryllium ion an upper limit of 69(30) mK can be given. This demonstration paves the way for further developments towards sympathetic laser cooling of HCIs. Furthermore, the optical access to the Penning trap was used for high-precision laser spectroscopy of the magnetic dipole fine structure transition in the ground state of boronlike argon ⁴⁰Ar¹³⁺ with an unsurpassed relative uncertainty of the absolute frequency of 9.4×10⁻⁹ . To this end, a novel spectroscopy scheme was demonstrated for the first time, which uses the CSGE and does not require a detection of fluorescence. This proof-of-principle method can be extended to other systems, opening up new possibilities to test BS-QED in the strongest electromagnetic fields by investigating the optical hyperfine structure in heavy HCI by means of laser spectroscopy.