BACKGROUND The generation and control of coherent electromagnetic waves, such as
those provided by electronic oscillators in the radio frequency domain or lasers in the optical …

“Quantum sensing” describes the use of a quantum system, quantum properties, or quantum
phenomena to perform a measurement of a physical quantity. Historical examples of …

Einstein's theory of general relativity states that clocks at different gravitational potentials tick
at different rates relative to lab coordinates—an effect known as the gravitational redshift. As …

We report an optical lattice clock with a total systematic uncertainty of 8.1× 10-19 in fractional
frequency units, representing the lowest uncertainty of any clock to date. The clock relies on …

Atomic clocks are vital in a wide array of technologies and experiments, including tests of
fundamental physics. Clocks operating at optical frequencies have now demonstrated …

We describe an optical atomic clock based on quantum-logic spectroscopy of the S 0 1↔ P
3 0 transition in Al+ 27 with a systematic uncertainty of 9.4× 10-19 and a frequency stability …

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 …

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