Tidal potential measured with distant optical clocks

Abstract

Fibre-linked optical clocks sense tidal changes of the gravitational potential, but separating overlapping tidal components and quantifying their precision remain challenging. Using strontium and ytterbium clocks 692 km apart, we measure over 353 days a response of 0.95 (0.11) to the combined solid-Earth and ocean-loading tide and 1.01 (0.13) for the lunar semidiurnal group, and separate the lunar and solar-frequency semidiurnal contributions. A signal-to-noise model based on the actual sampling accounts for the lunar precision and guides future clock-network observations.