Isotope shift measurements in highly charged calcium

Highly charged ions (HCI) are promising candidates for novel optical clocks and tests of fundamental physics. For example, many HCI possess ultra-narrow optical transition that show a large sensitivity to variation of the fine-structure constant, exceeding the sensitivity of singly charged ions. They also provide additional narrow optical transitions that can be used for new physics searches using isotope shift measurements. The megakelvin temperatures needed to produce HCI usually foreclose high-resolution spectroscopy of HCI but recent experimental advances overcame those problems. In our experiment, we extract HCI from an electron beam ion trap (EBIT) and transfer them to a cryogenic linear Paul trap. There, single HCI are sympathetically cooled by laser-cooled Be ions down to millikelvin temperatures, thus enabling quantum logic state readout. This allowed to demonstrate the first optical clock based on Ar XIV, and the determination of its absolute frequency with sub-Hz uncertainty. In this thesis, we apply the developed techniques to the fine structure transition in Ca XV at a wavelength 570 nm and present isotope shift (IS) measurements between all five stable and even isotopes of calcium (40, 42, 44, 46, 48). The measurements required additional hardware for the experimental apparatus that we will present. For loading from solid targets, a laser ablation source for the EBIT system was developed and installed. For frequency stabilization of the clock laser, a vibration-insensitive cubic cavity was setup. Additionally, in parallel to the IS measurements we commissioned an updated version of the cryogenic Paul trap which was installed and characterized after the IS measurements were finished. We determine the absolute transition frequency of each isotope by an optical clock comparison with the Yb octupole clock at PTB. From those measurements we derive the isotope shifts of the transition with an uncertainty of 150 mHz. We combine these results with available isotope-shift data of singly charged Ca in a King plot. This analysis is sensitive to a new force that would couple electrons and neutrons. In this way, we tighten the bounds on the existence of such a hypothetical interaction compared to previous studies. We also discuss how far improved measurements of Ca isotope masses and isotope shifts of the will affect the King plot and the bounds on new physics that can be extracted from it.