Scientists have manufactured the world's smallest atomic clock, with inner machinery about the size of a grain of rice. Requiring very little power to run, the device loses only one second every 300 years and could one day provide precise timekeeping for portable applications such as wireless communication devices and Global Positioning System (GPS) receivers.

Like other atomic clocks, the new design relies on the natural vibrations of cesium atoms, which tick 9.2 billion times each second. John Kitching of the National Institute of Standards and Technology and his colleagues trapped cesium vapor inside a chamber that is probed by a tiny laser, resulting in two electromagnetic fields. The team then adjusted the fields until the difference between them equaled that of the energy levels within the cesium atoms, causing the atoms to stop absorbing or emitting light. An external oscillator was then stabilized against the natural resonance frequency of cesium. The real power of our technique is that we're able to run the clock on so little electrical power that it could be battery operated and that it's small enough to be easily incorporated into a cell phone or some other kind of handheld device, explains Kitching. And nothing else like it even comes close as far as being mass producible.

Although it's about 100 times smaller, the minuscule clock is not as accurate as larger atomic clocks, which can reach up to two meters in height. But it could still offer a nearly 1,000-fold improvement in long-term precision compared to quartz crystals currently used for small-scale applications. The researchers describe the novel clock in the latest issue of Applied Physics Letters.