This month, NIST scientists officially submitted it to the International Bureau of Weights and Measures (BIPM) for certification as a “primary frequency standard,” a title reserved for the most elite atomic clocks on the planet.
Only around ten countries operate such clocks — now the U.S. is back in that top tier.
How the clock works
Unlike regular clocks, atomic clocks like NIST-F4 keep time using the natural vibrations of atoms — in this case, cesium atoms.
Inside the clock, thousands of these atoms are cooled to near absolute zero using lasers and then tossed upward in a fountain-like motion.
As they rise and fall, they pass through microwave radiation tuned to a frequency that makes the atoms shift their energy state — a transition that defines the “tick” of the clock.