Fountain clocks, developed in the 1980s, represent the pinnacle of atomic timekeeping technology. These clocks use laser-cooled cesium or rubidium atoms to achieve unprecedented precision, measuring time with an accuracy of one second in 100 million years. The process involves cooling atoms to near absolute zero, then using microwaves to measure their resonant frequency, which defines the official international second.
Fountain clocks are more sensitive than beam clocks due to their longer interaction time with atoms, allowing for more precise measurements. However, they are complex and expensive, with fewer than 30 existing worldwide. Currently, only 10 countries contribute data from fountain clocks to the International Bureau of Weights and Measures for calibrating universal coordinated time.
While fountain clocks are not used for continuous timekeeping, they serve as the primary reference for calibrating other clocks and time scales used by the public. Their development has enabled the redefinition of most fundamental physical units in terms of the second, demonstrating their critical role in modern metrology.
Source: https://www.nist.gov/atomic-clocks/fountains-atoms-exquisite-timekeepers
Keywords: cesium, microwaves, resonant frequency, laser-cooled, fountain clock
