Overview
- The PTB and TU Wien team operated a closed feedback nuclear clock that used the Th‑229 resonance in a millimetre‑scale CaF2 crystal to steer a continuous 148 nm laser and ran unattended for over 24 hours on Wednesday.
- Measured instability followed roughly 3×10⁻¹² divided by the square root of measurement time and approached the 10⁻¹⁵ level after a day, a performance that is promising but still below the world’s best optical atomic clocks.
- The experiment was validated by sending an optical signal over a stabilized fibre link to an Ytterbium ion clock at BEV and was used in a 23‑hour search for periodic frequency shifts expected from some ultralight dark‑matter models, yielding no significant signal and new upper limits on certain couplings.
- Researchers identified host‑crystal issues as the main technical limit: local stresses and inhomogeneities in the CaF2 caused run‑to‑run resonance shifts of about 5×10⁻¹³, and improving crystal homogeneity and stronger vacuum‑UV lasers are the next clear engineering steps.
- An independent Chinese group published a near‑simultaneous demonstration of a functional Th‑229 nuclear clock, showing the approach is reproducible and setting the stage for efforts to scale the technology toward compact clocks for navigation, metrology, and fundamental‑physics tests.