A cryogenic Paul trap for probing the nuclear isomeric excited state 229 m Th 3 + .

Abstract: While laser excitation of the nuclear isomeric transition in 229 Th has been recently achieved for thorium atoms embedded in large-bandgap crystals, laser excitation and characterization of the nuclear transition in trapped 229 Th 3 + ions has not yet been accomplished. To address these experiments, a cryogenic Paul trap setup has been designed, built, and commissioned at LMU Munich. Here, we present the specifications of the new experimental platform and demonstrate its successful operation, showing the extraction, subsequent ion guiding, mass purification, and trapping of 229 Th 3 + and 229 m Th 3 + ions from a newly designed buffer-gas stopping cell as well as of 88 Sr + ions from laser ablation of a solid target. Further, we show sympathetic laser cooling of 229 (m) Th 3 + by Doppler-cooled 88 Sr + ions and the formation of mixed-species Coulomb crystals.