Overview
- The Vienna and Tsinghua teams, which posted arXiv preprints Monday, reported independent prototypes that lock vacuum‑ultraviolet lasers to a low‑energy nuclear transition in thorium‑229 and operate at room temperature.
- The Vienna prototype ran as a complete stand‑alone clock, was compared directly to an established ytterbium‑ion atomic clock, and was used in an initial search for ultralight dark matter that found no signal.
- Tsinghua tested their approach in two independently produced calcium‑fluoride crystals and measured nearly identical resonance frequencies with fractional instability approaching about 1×10⁻¹¹ after one day.
- Both teams embed thorium‑229 in calcium fluoride because its unusually low‑energy nuclear transition can be driven with UV light and is intrinsically less sensitive to external electromagnetic noise than electron transitions; however, the results are preprints, do not yet beat the best atomic clocks, and require improvements in lasers, crystals, and electronics and independent peer review.
- The idea dates to a 2003 proposal and follows 2024 laboratory demonstrations of the transition, and if matured the solid‑state nuclear clocks could enable smaller satellite clocks, tighter tests of fundamental constants and dark‑matter couplings, and higher‑precision geodesy.