Microfabricated atomic clocks

We summarize the development of microfabricated atomic frequency references at NIST. The physics packages of these devices have volumes near 10 mm/sup 3/ and power dissipation below 150 mW, and can potentially achieve a fractional frequency instability in the range of 10/sup -11/ over long periods. A fully integrated frequency reference could find application in portable, battery operated devices such as global positioning system (GPS) receivers and cellular telephones.