History of the Atomic Clock

1879, Lord Kelvin suggests idea of using atomic transitions to measure time

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 made by Harold Lyons

Professor Norman Ramsey invented the separated oscillatory field method of molecular beam magnetic resonance spectroscopy

1951, NIST completes the first direct measurement of the cesium hyperfine separation with the atomic beam technique with NBS-1

1952, NIST completes the first accurate measurement of the frequency of the cesium hyperfine separation with NBS-1 (Lyons and his successor Polykarp Kusch and Jesse Sherwood)

1953, Professor Robert H. Dicke describes method for extending time of interaction of atomic particles with electromagnetic field by use of a selected gas to provide a medium in which diffusion limits the rate of movement of the active atomic particles (buffer gas)

1954,

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

August, first atomic beam clock (according to the IEEE): Professor Jerrold R. Zacharias’s (“Zach”) cesium atomic beam frequency standard at MIT’s Molecular Beam Laboratory of the Research Laboratory of Electronics (originally the Radiation Laboratory) was put into operation, first to be in feedback loop with external oscillator (quartz) using a servo control system. Features:

development of an efficient cesium beam source
development of "Stabilivac" titanium evapor-ion pump to permit operation of cesium atomic beam apparatus without cumbersome mechanical pump in combination with a diffusion pump
development of electronic circuits to permit operation with a quartz oscillator "locked" to the cesium resonance

Zach testifies at Oppenheimer’s AEC security hearing and negotiates agreement for commercial development of his atomic beam clock at the National Company

1955

Louis Essen and Jack Parry of the National Physical Laboratory in England builds the first cesium-beam resonator used as a calibration source and determine a new value for the cesium hyperfine transition frequency based on the uniform time scale maintained by the Royal Greenwich Observatory, 9192.63183 MHz. It was calibrated with Dr. William Markowitz’s (Director of Time Service of USNO) ET time scale. Although never operated as an atomic clock or used in a feedback loop with a stabilized oscillator, some say it is the first cesium-based atomic clock.

Natco’s (National Company’s) atomic beam clock, aka ABC, become known to be the National Atomic Frequency Standard or NAFS

1956, October, MIT, J. R. Zacharias, and R. T. Daly of National Company, Inc. present the “Atomichron” (previously known as the NAFS), the first commercial atomic clock

1958

9,192,631,770 Hz value determined with the NPL standard by Essen and Markowitz

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

1959, NBS-1 goes into regular service as NIST's primary frequency standard.

1960

First atomic hydrogen maser was constructed by Goldenberg, Kleppner and Ramsey and its successful operation at Harvard as a free running oscillator was reported

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

1962, Robert Vessot and his associates, H. Peters and J. Vanier at Varian Associates in Beverly, Massachusetts, in collaboration with Professor Ramsey and Dr. Kleppner undertook the development of a commercial hydrogen maser

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

1964, Cesium atomic beam tubes developed by Varian Associates for Hewlett Packard (12 in long) and incorporated into the HP 5060 Cesium Atomic Beam Frequency Standard by Dr. Leonard Cutler and his associates (became one of the most widely used atomic frequency standards in the world)

1965, first units of commercial hydrogen maser: Varian Model H-10 Hydrogen Maser Frequency Standard

1967

The 13th General Conference on Weights and Measures defines the second on the basis of vibrations of the cesium atom (see 1958); second no longer has an astronomical basis.

HP 5061 manufactured

1968, NBS-4 is completed and used into the 1990s as part of the NIST time system

1971, October, Joseph C. Hafele, physicist, and Richard E. Keating, astronomer, took four cesium-beam clocks aboard commercial airliners to test the theory of relativity: the Hafele – Keating experiment

1972, NBS-5 is completed and serves as the primary standard.

1975, NBS-6 begins operation (neither gaining nor losing one second in 300,000 years)

1989, The Nobel Prize in Physics is awarded to three researchers: Norman Ramsey of Harvard University, Hans Dehmelt of the University of Washington and Wolfgang Paul of the University of Bonn for their work in the development of atomic clocks. NIST’s work is cited as advancing their earlier research.

1991, HP 5071 manufactured, was microprocessor-based (manufacturing switched to Agilent and then Symmetricon) and has accuracy of 2 × 10-13

1993, NIST-7 is created (achieves uncertainty of 10-15, or 20 times more accurate than NBS-6)

1999, NIST-F1 begins operation with uncertainty of 1.7 x 10-15, accuracy: one second in 20 million years

2014, NIST launched NIST-F2