The heart of a minuscule atomic clock—believed to be 100 times smaller than any other atomic clock—has been demonstrated by scientists at the Commerce Department’s National Institute of Standards and Technology (NIST), opening the door to atomically precise timekeeping in portable, battery-powered devices for secure wireless communications, more precise navigation and other applications.
Described in the Aug. 30, 2004, issue of Applied Physics Letters, the clock’s inner workings are about the size of a grain of rice (1.5 millimeters on a side and 4 millimeters high), consume less than 75 thousandths of a watt (enabling the clock to be operated on batteries) and are stable to one part in 10 billion, equivalent to gaining or losing just one second every 300 years.
In addition, this “physics package” could be fabricated and assembled on semiconductor wafers using existing techniques for making micro-electro-mechanical systems (MEMS), offering the potential for low-cost mass production of an atomic clock about the size of a computer chip and permitting easy integration with other electronics. Eventually, the physics package will be integrated with an external oscillator and control circuitry into a finished clock about 1 cubic centimeter in size.
“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,” says physicist John Kitching, principal investigator for the project. “And nothing else like it even comes close as far as being mass producible.”
The mini-clock is comparable in size and long-term stability to temperature-compensated quartz crystal oscillators, currently used in portable devices. NIST scientists expect to improve the clock’s long-term stability and reduce its power consumption to the point where the device could substantially improve the performance of many commercial and military systems that require precision time keeping.