Long-Term Frequency Instability of a Portable Cold 87Rb Atomic Clock

This paper presents measurements of the long-term frequency stability of a cold Rubidium 87 atomic clock that is under development at SpectraDynamics for the Defense Advanced Research Projects Agency (DARPA) Portable Microwave Cold Atomic Clock Small Business Innovative Research (SBIR) effort. The clock output at 5 MHz has been compared with the UTC (NIST) timescale over a period of several weeks. Analysis of the sources of frequency instability is presented. The portable clock is about the size of a desktop computer (22x37x32 cm) and weighs 28kg.