{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"4aaebe1a5646b14dc53784b26a2502fc0361e3335ff98033cca3769f36204c09","created":"2026-10-15T23:43:22Z","files":[],"origin":{"assisted_by":["ai:gpt-5.5"],"kind":"seed"},"parents":["1c75c8063c36a7d6c08cdba885f650c4cc05bacbdb506ada402b318843a6fa7c","ce59fb6cd812fc05906d0c60a71c75ea22bc686bcf38e7c3ef7010834d98ee7b"],"salt":"bc00956b88e96dbbf4d20ab79349dff2350931ce3c9c0538f4676533541cd65a","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"identification","assisted_by":["ai:gpt-5.5"],"external_id":"amo.optical-clocks-second.solid-state-nuclear-clock","kind":"well-posed","literature_status":"open","n":"2","parents":[],"plain":"Thorium-229 nuclei embedded in a transparent crystal can be laser-excited, which could make a clock that is compact and insensitive to many disturbances. The crystal environment broadens and shifts the line, and the ultimate accuracy is unknown.","posed_since":"","precise":"For Th-229 in $\\mathrm{CaF_2}$, $\\mathrm{LiSrAlF_6}$ or $\\mathrm{ThF_4}$ hosts, identify the mechanisms (temperature-dependent electric-field gradients, inhomogeneous broadening from charge-compensating defects, isomer quenching by radiation-induced defects) limiting linewidth and frequency reproducibility, and determine the achievable fractional uncertainty of a solid-state nuclear clock.","problem_ref":"1c75c8063c36a7d6c08cdba885f650c4cc05bacbdb506ada402b318843a6fa7c","references":"","settled_by":"Repeated measurements across crystals and temperatures with a closed-loop nuclear clock compared to an optical clock, giving a reproducibility budget below $10^{-17}$.","status_note":"Temperature sensitivity was measured in 2024, crystal-to-crystal reproducibility in 2025, and a Th-229 nuclear clock with feedback loop was reported in June 2026.","title":"What limits the accuracy of a solid-state thorium nuclear 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