Quantum theory has been successfully validated in numerous laboratory experiments. But
would such a theory, which effectively describes the behavior of microscopic physical …

We review experimental progress on optical atomic clocks and frequency transfer, and
consider the prospects of using these technologies for geodetic measurements. Today …

This paper outlines the roadmap towards the redefinition of the second, which was recently
updated by the CCTF Task Force created by the CCTF in 2020. The main achievements of …

The passage of time is tracked by counting oscillations of a frequency reference, such as
Earth's revolutions or swings of a pendulum. By referencing atomic transitions, frequency …

A clock at a higher altitude ticks faster than one at a lower altitude, in accordance with
Einstein's theory of general relativity. The outstanding stability and accuracy of optical …

Optical atomic clocks require local oscillators with exceptional optical coherence owing to
the challenge of performing spectroscopy on their ultranarrow-linewidth clock transitions …

Rapid progress in optical atomic clock performance has advanced the frontiers of
timekee**, metrology and quantum science,–. Despite considerable efforts, the …

Optical atomic clocks, due to their unprecedented stability,–and uncertainty,,–, are already
being used to test physical theories, and herald a revision of the International System of …

Ultrastable lasers are essential tools in optical frequency metrology enabling unprecedented
measurement precision that impacts on fields such as atomic timekee**, tests of …

A list of standard reference frequency values (LoF) of quantum transitions from the
microwave to the optical regime has been recommended by the International Committee for …