BASE - Annual Report 2022

This report summarizes the progress made by the BASE collaboration in 2022. It contains short summaries of the main manuscripts produced. One of these manuscripts reports on a 16-parts-per-trillion comparison of the proton-to-antiproton charge-to-mass ratio. This measurement improves the previous best limit by a factor of 4.3, and contains the first-ever performed clock-based differential test of the weak equivalence principle with protons and antiprotons. Another manuscript sets stringent limits on the parameter-space for the existence of millicharged particles , based on heating rate measurements in the BASE analysis trap. The third manuscript studies sympathetic cooling schemes for separately trapped ions coupled via image currents, while the fourth manuscript reports on the successful implementation of ultra-sensitive frequency tuneable detection circuits developed for the axion haloscope BASE-CDM. In the main work carried out in 2022, the group focused on the commissioning of an experiment dedicated to measure the antiproton magnetic moment with a fractional precision at a level of about 100 parts in a trillion. This includes the setup of a new trap stack, the development of revised cryogenic experiment electronics and superconducting single particle detectors, as well as the implementation and characterization of a new magnet shimming and shielding system. In addition parametric resonance studies with single particles have been carried out to characterize the analysis- and cooling traps of the experiment. Throughout the year, new cooling techniques were established that improve the sampling performance of the experiment by more than a factor of 60. This led to the non-destructive observation of single proton spin flips with a spin initialization fidelity $>99\,\%$, and a precision trap spin state detection fidelity of $94(3)\,\%$. Eventually, the 2022 run culminated in the non destructive detection of proton spin-quantum transitions that were induced in the homogeneous precision trap of the multiple trap experiment, which paves the path towards magnetic moment measurements with sub-p.p.b. resolution.