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A New Era for Atomic Clocks

February 4, 2014

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Contact: Laura Ost
(303) 497-4880


NIST's first atomic clock
Credit: NIST

Atomic clocks keep time based on the natural oscillations (or frequencies) of atoms, which are much more stable and accurate than any mechanical devices. The atomic clock was invented at NIST in 1949 (then the National Bureau of Standards), and atomic clocks quickly became more accurate than any other timekeeping technologies.

Atomic clocks began to have notable impacts on other technologies about 20 years later. Atomic time standards have been in use since 1967, when one of the cesium atom’s natural frequencies was selected by an international committee as the basis for the international unit of time, the “SI second”. The second is defined as exactly 9,192,631,770 oscillations or cycles of this cesium atom resonant frequency. NIST operates two U.S. civilian time and frequency standards based on cesium: NIST-F1 keeps time to within 1 second in about 100 million years as of 2013, and NIST-F2, introduced in early 2014, is about three times better at plus or minus 1 second in about 300 million years.


Beyond Timekeeping


For example, the frequency (“ticking rate”) of atomic clocks is altered slightly by gravity, magnetic fields, electrical fields, force, motion, temperature and other phenomena. In today’s conventional atomic clocks, those frequency changes are errors to be tightly controlled. In next-generation atomic clocks, the frequency changes are measured to such a fine degree that the clocks could become world-class instruments for measuring gravity, magnetic and electrical fields, force, motion, temperature and many other quantities.

Jun Ye
JILA/NIST Fellow Jun Ye and the strontium lattice clock.
credit: J. Burrus/NIST



The suitability of various clocks for different applications can also be seen in recent history. For example, the aluminum ion logic clock’s world-record timekeeping performance was due in part to this clock’s insensitivity to changes in magnetic fields, electrical fields, and temperature. This insensitivity is highly desirable for the best timekeeping results. But it also means the aluminum ion clock is not a good candidate for measuring magnetic and electrical fields or temperature, whereas other NIST atomic clocks have greater sensitivity to those quantities.

*JILA is the joint research and training institute of NIST and the University of Colorado Boulder.


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