Portable Microwave Cold Atomic Clock

We present the design of a small, portable, microwave cold atomic clock that meets the frequency stability requirement of<1X10-12 at 1 s averaging time and < 5X10-15 for an averaging time of 1 day in a volume less than 1 liter, mass less than 1kg, and power goal of less than 5W. 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, thereby 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. The proposed clock requires no vacuum pumps.The load/Ramsey/detect sequence takes 100ms/78ms/14ms so that the duty cycle is better than 40%, helping with problems caused by the Dick effect.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.