Sprecher
Beschreibung
Metallic-magnetic microcalorimeter detectors for X-ray precision spectroscopy provide excellent energy
resolution combined with a broad bandwidth acceptance. This opens up new experimental possibilities, in
particular for bound-state QED studies in highly charged ions. Using a pair of such detector systems, we
recently conducted a landmark experiment, as presented in [P. Pfäfflein et al. Quantum electrodynamics
in strong electromagnetic fields: Substate resolved Kα transition energies in helium-like uranium, PRL
134, 153001 (2025)].
At CRYRING@ESR, we recorded the X-ray spectra for the electronic transitions into the ground- and
excited states for electron-cooled, helium-like uranium (U90+) ions. This provided us with an unmatched
spectral resolution close to 90 eV FWHM. That enables to resolve and to determine precisely the four
components of the Kα groundstate transitions. The results are in good agreement with state-of-the-art
bound-state QED calculations for the strong-field regime. In this contribution, we will present a summary
of this measurement as well as a first glance at data obtained in a follow-up experiment conducted this
summer.
