PHARAO: A Space Clock with Cold Cesium Atoms

摘要

We describe a cold atom clock designed for operating in microgravity, the PHARAO project. Preliminary results have already been obtained on earth and the prototype will be tested in the reduced gravity of aircraft parabolic flights in the beginning of 1997. The PHARAO prototype is an extension of the work done at the BNM-LPTF on a cesium atomic fountain, which presents a resonance linewidth of 700 millihertz, a frequency stability of 1.5 x 10E-13 TauE-1/2 where tau is the integration time in seconds. The accuracy of the fountain clock is presently 2 x 10E-15, more than three times better than previously achieved with uncooled conventional devices. The expected relative stability of the PHARAO cesium clock in space is about 3 x 10E-14 at one second or 10E-16 per day. Because the reduced gravity environment allows a mode of operation of the clock different from earth fountains, the accuracy of PHARAO should surpass that of fountains and be in the 10E-17 range. The PHARAO frequency standard could be a key element in future space missions in fundamental physics such as SORT (Solar Orbit Relativity Test), detection of gravitational waves, or for the realization of a global time scale and a new generation of positioning system.