AIBRIEF
A new lutetium 176 optical clock, built around a radioactive rare earth atom, reports a precision roughly four times better than any prior clock, while redefining the SI second remains years away.
A lutetium-176 optical clock has reported the sharpest evaluated systematic uncertainty ever published for an atomic clock: 1.2 × 10⁻¹⁹ for one system and 1.3 × 10⁻¹⁹ for a second, with 1.0 × 10⁻¹⁹ on their difference. That is roughly four times better than the prior record, the authors write.
Lutetium-176 is a radioactive form of the rare metal lutetium. Its large atomic mass and hyperfine averaging make it comparatively insensitive to magnetic fields and ambient thermal radiation, the practical reason the new measurement can hold its precision over days.
The two systems were not independently operated. A single shared clock laser interrogated both, and correlation spectroscopy stripped common-mode phase noise from the comparison. Across 11 runs totaling 200 hours, the weighted mean frequency difference was −0.1 ± 5.7 (statistical) ± 1.0 (systematic) × 10⁻¹⁹. The paper recorded 8.3 days of measurement over a 12.4-day window, 67% uptime, at room temperature with commercially available lasers.
That gives fundamental-physics tests, including searches for drifting constants and dark-matter signatures, a sharper instrument. Whether the SI second, defined since 1968 by cesium-133 and managed by the International Bureau of Weights and Measures, gets redefined is a separate, years-to-decades institutional question.