History of Atomic Clock

Return Time Standards

1945 Isidor Rabi, a physics professor at Columbia University, suggests a clock could be made from a technique he developed in the 1930's called atomic beam magnetic resonance.

1949 Using Rabi’s technique, NIST (then the National Bureau of Standards) announces the world’s first atomic clock using the ammonia molecule as the source of vibrations.

1952 NIST announces the first atomic clock using cesium atoms as the vibration source. This clock is named NBS-1.

1954 NBS-1 is moved to NIST’s new laboratories in Boulder, Colo.

1955 The National Physical Laboratory in England builds the first cesium-beam clock used as a calibration source.

1958 Commercial cesium clocks become available, costing $20,000 each.

1960 NBS-2 is inaugurated in Boulder; it can run for long periods unattended and is used to calibrate secondary standards.

1963 The search for a clock with improved accuracy and stability results in NBS-3.

1967 The 13th General Conference on Weights and Measures defines the second on the basis of vibrations of the cesium atom; the world’s timekeeping system no longer has an astronomical basis.

1968 NBS-4, the world’s most stable cesium clock, is completed. This clock was used into the 1990s as part of the NIST time system.