Lutetium atomic clock reaches reported uncertainty of 1 x 10-19

Researchers at Singapore's Centre for Quantum Technologies report an uncertainty of 1 x 10-19 for a lutetium atomic clock, the lowest reported for an optical atomic clock. They measured its frequency to 19 decimal places and compared two clocks that agreed to an uncertainty of 5.7 x 10-19. The clock counts light oscillations matched to an energy change in a lutetium ion. That transition is relatively insensitive to temperature and magnetic-field changes. The instrument remains laboratory-scale, and gravitational differences between distant locations are not yet known precisely enough to compare clocks at this level.