The World's Smallest Atomic Clock

The world's smallest atomic clock, about the size of a rice grain, is built around a microcell about 1 mm³ in volume filled with cesium atoms. It draws only about 30 mA of current from a 2.5 V battery. Atomic clocks are the best timekeepers because they are able to convert the high-precision information contained in the light emitted by alkali atoms (the light emerging from an atomic transition from one energy level to another can be measured to an uncertainty of better than a part in a billion) into a usable standard for defining the second.

The new miniature clock has a precision of 3.5 x 10^-10. What this means is that events can be timed with an uncertainty of about one part in 3 billion. Scientists at NIST in Boulder, Colorado make atomic clocks that are far more precise---the F-1 clock is good to about one part in 10 trillion---but this requires a huge table-top’s worth of equipment. The mini version being reported now should eventually reach a stability of about 10^-11, some 10,000 times better than any quartz oscillator clock of equivalent size and power.

How will this new cheap, tiny, low-power, high-precision MEMS clock be used? In satellites, GPS receivers, networked computer CPU’s, possibly in cell phones. (Knappe et al., Applied Physics Letters, 30 August 2004; contact John Kitching, kitching@boulder.nist.gov, 303-497-3328; for an explanation of precision and accuracy, see NIST Time & Frequency glossary.)