Thorium-229 Nuclear Transition Realized in Prototype Clock at JILA with 10^-17 Stability

The experiment used a VUV frequency comb to excite the nuclear transition in laser-cooled thorium ions embedded in a solid-state host, bypassing the need for a full ion trap array. Frequency measurements against a strontium optical clock yielded a fractional uncertainty of 1.2 imes 10^-17 after 30 hours of averaging, confirming the transition's narrow linewidth below 10^-4 Hz.

This leap matters because nuclear transitions are far less sensitive to external electromagnetic fields than electronic states in atomic clocks, promising reduced systematic errors for GPS augmentation and tests of fundamental constants. Prior optical clock work focused on electron shells; the nuclear approach directly probes strong-force physics and offers new channels for ultralight dark matter detection that electron-based systems cannot access.

The original coverage underplayed the solid-state host's decoherence risks and the absence of a closed-loop servo. A full portable clock still requires chip-scale VUV sources and cryogenic operation, neither of which exist yet. Next milestones include integrating the transition with existing Sr/Yb combs and demonstrating 10^-19 stability in a multi-ion array within three years.