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Incoming links: Ramsey separated oscillatory fields experiment
Atomic clock Created 2026-10-14 Updated 2026-10-18
An atomic clock uses an atomic transition as a frequency reference for an oscillator; counting its calibrated cycles realizes a time interval. In a passive beam implementation, the chemical atoms are repeatedly prepared, interrogated and detected, while feedback control corrects the continuously running oscillator. The Ramsey separated oscillatory fields experiment explains how internal quantum phase becomes a measurable population signal.
The SI second fixes the unperturbed ground state hyperfine structure transition frequency of caesium-133 to exactly . This is a defining value for the ideal transition, rather than a guarantee that an operating apparatus has no shifts.[ref]
SI base unit: second (s) by Bureau International des Poids et Mesures. SI base unit: second (s), defining paragraph and equivalent duration in periods of the unperturbed caesium-133 ground-state hyperfine transition