The article discusses the development of atomic clocks at NIST, focusing on the evolution from room-temperature cesium clocks to laser-cooled fountain clocks. Key points include:
1. Room-temperature cesium clocks had limited accuracy due to atoms moving at hundreds of meters per second, causing “blurry” energy transitions.
2. NIST researchers developed laser cooling techniques to slow atoms to a few centimeters per second, enabling more precise microwave probing.
3. The first laser-cooled fountain clock was built in 1999 (NIST-F1) with an accuracy of one second in 20 million years.
4. NIST-F2, launched in 2014, achieved even greater accuracy (one second in 300 million years) but required liquid nitrogen cooling.
5. NIST-F2 and NIST-F1 served as primary frequency standards for calibrating Coordinated Universal Time until 2015.
6. NIST is currently evaluating new fountain clocks (NIST-F3 and NIST-F4) for international timekeeping contributions.
7. Hyper-accurate atomic clocks have enabled precise timekeeping applications in finance, power grids, and communications.
The article highlights NIST’s leadership in atomic clock development and its impact on realizing the SI second and other fundamental units.
Source: https://www.nist.gov/si-redefinition/second-present
Keywords: absolute zero, fountain clock, NIST-F2, atomic clock, SI unit
