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-topís 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 CPUís, possibly
in cell phones. (Knappe
et al., Applied Physics Letters, 30 August 2004; contact
John Kitching, email@example.com, 303-497-3328; for an explanation
of precision and accuracy, see NIST
Time & Frequency glossary.)