Tiny Timepiece: Atomic clock could fit almost anywhere

Physicists have shrunk the high-tech heart of an atomic clock to the size of a rice grain. This dramatic miniaturization may lead to widespread use of atomic clocks in battery-powered devices such as global positioning system (GPS) receivers, wireless computers, and cell phones, says John Kitching, leader of the National Institute of Standards and Technology (NIST) team in Boulder, Colo., that created the minuscule prototype.

LIGHTHEARTED. A laser at the bottom of this rice-grain-tall tower of high-tech components fires through a chamber of atomic vapor within the stack. The result is a signal that could be used to tune an atomic clock the size of a sugar cube. NIST

The itsy device includes a transparent chamber containing a vapor of cesium atoms, a laser, a photodetector, heaters, and optical lenses and filters—all in a package small enough to fit on a microchip. Kitching and his colleagues describe the gadget in the Aug. 30 Applied Physics Letters.

“This is an important demonstration of a critical component for use in a chip-scale atomic clock,” comments Christopher R. Ekstrom of the U.S. Naval Observatory in Washington, D.C.

Many portable electronic items already contain on-chip clocks regulated by oscillations of quartz crystals. However, the frequencies of those oscillations vary much more over time and with temperature fluctuations than do frequencies of atomic clocks.

Military planners foresee a boon from developing atomic replacements for quartz timekeepers. For instance atomic clock–based GPS receivers would be less vulnerable than existing models to barrages of radio waves that enemies use to jam navigation instruments.

Although civilian payoffs are less obvious, better synchronization between networked computers and helping prevent eavesdropping on cell phone conversations might create markets for the diminutive atomic clocks, says Kitching.

The NIST team built its prototype with funding from the Defense Advanced Research Projects Agency (DARPA). The organization is pushing the development of tiny atomic clocks that could be cheaply mass-produced using techniques akin to those employed by makers of microelectronics.

Several DARPA-supported teams, including Kitching’s, are pursuing the goal of building a sugar-cube-size atomic clock that could run off the power equivalent of a single AA battery. Today’s smallest atomic clock takes up as much space as a cigarette pack and can’t run on battery power (SN: 9/9/95, p. 175).

So far, the NIST team has built, on a lilliputian scale, the part of an atomic clock that accepts a high-frequency oscillation from another part of the clock and compares it to a natural electromagnetic frequency of atoms of a specific element. A full clock requires two additional pieces: the oscillator and the control electronics.

While the NIST package is petite enough, it remains too power hungry. It’s also a long way from the DARPA timekeeping goal of erring by less than 1 microsecond per day. Still, the NIST team has “put together something that shows feasibility. That’s very commendable,” comments physicist R. Michael Garvey of Symmetricom. That Beverly, Mass.–based atomic clock maker is part of a DARPA-funded team competing with the NIST group.

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