Portable Microwave Cold Atomic Clock

We present the design of a small, portable, microwave cold atomic clock that meets the frequency stability requirement of < 8X10-13 at 1 s averaging time and < 3X10-15 for an averaging time of 1 day. The entire clock is about the size of a desktop computer 18.75 ” X 14.75 ” X 8.77 ” (47.6 cm X 37.5 cm X 22.3 cm) and weighs 30.5 kg. The clock can run on both 100-240 VAC as well as +24 VDC. Steady state power consumption is 75 W. The clock outputs 100 MHz, 10 MHz, 5 MHz and 1 PPS with synchronization capability. The approach is a cold atom clock based on laser-cooled 87Rb atoms trapped and dropped under the influence of gravity. The laser system requires no ability to launch atoms, resolving serious technical limitations inherent in fountain designs. The laser light is not mechanically shuttered, and the light shift is controlled by other means. The repump is provided by RF sidebands on the laser, eliminating the repump laser as a source of AC Stark shift. An ultra-low noise high performance miniature RF synthesizer is used for microwave interrogation and miniaturized custom electronics are used to control the laser system.