Compact, Highly Stable Ion Atomic Clock

A mercury-ion clock now at the breadboard stage of development (see figure) has a stability comparable to that of a hydrogen-maser clock: In tests, the clock exhibited an Allan deviation of between 2 × 10–13 and 3 × 10–13 at a measurement time of 1 second, averaging to about 10–15 at 1 day. However, the clock occupies a volume of only about 2 liters — about a hundredth of the volume of a hydrogen- maser clock. The ion- handling parts of the apparatus are housed in a sealed vacuum tube, wherein only a getter pump is used to maintain the vacuum. Hence, this apparatus is a prototype of a generation of small, potentially portable high-precision clocks for diverse ground- and space-based navigation and radio science applications. Furthermore, this new ion-clock technology is about 100 times more stable and precise than the rubidium atomic clocks currently in use in the NAVSTAR GPS Earth-orbiting satellites.