Lowest Evaluated Systematic Fractional Uncertainty of an Optical Atomic Clock

Lu-1 lutetium-ion optical clock

A 2026 Nature study reported two lutetium-176 single-ion optical frequency references. Lu-1 achieved a reported evaluated fractional systematic frequency uncertainty of 1.2 × 10⁻¹⁹, while a separate same-species comparison independently tested the two references at a different precision.