Singapore team achieves 19-digit accuracy in lutetium atomic clock comparison
Researchers at the National University of Singapore (NUS) have developed a pair of optical atomic clocks using lutetium ions that achieve a fractional frequency uncertainty of 1 × 10⁻¹⁹. By comparing two independent systems over 200 hours, the team verified agreement to the 19th decimal place, marking a fourfold improvement over previous records. This precision enables millimeter-scale gravity measurements and supports the potential redefinition of the SI second.