{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"87a713b4e2c7874a61284fccf5abd72b4492558dd7cfa27135477e7655a12924","created":"2026-10-03T07:17:54Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"23c41392366d154eda25c848173674755b7d48b41d24bf5c62e934ee894fdded","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"yes-no","assisted_by":[],"external_id":"amo.optical-clocks-second.trapped-ion-nuclear-clock","kind":"well-posed","literature_status":"open","n":"1","parents":[],"plain":"Thorium-229 nuclei have been excited by laser inside crystals, but a single thorium ion held in a trap would avoid crystal disturbances and could make a clock accurate to about one part in $10^{19}$. Laser excitation of the nucleus in a trapped ion has not yet been achieved.","posed_since":"2003","precise":"Drive the $8.36\\,\\mathrm{eV}$ ($148.4\\,\\mathrm{nm}$) Th-229 isomer transition with a laser in a trapped, sympathetically cooled Th-229 ion (Th3+, whose single valence electron allows laser cooling and state detection, or higher charge states), detect excitation through the hyperfine structure of the electronic transitions, and determine the achievable systematic uncertainty of the resulting clock, predicted to approach 1e-19 (Campbell et al, Physical Review Letters, 2012).","problem_ref":null,"references":"","settled_by":"Observation of laser-driven isomer excitation in a trapped Th-229 ion, followed by a closed-loop clock operation with an evaluated systematic uncertainty budget.","status_note":"Trapped-ion work up to mid-2026 is theoretical or uses isomers populated in the alpha decay of U-233; a 2026 analysis (arXiv 2604.27614) estimates that locating the line in trapped Th3+ takes about one month with existing vacuum-ultraviolet lasers.","title":"Laser excitation of the Th-229 nuclear isomer in a trapped 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