Out of this world: The future of atomic clocks

Summary form only given. The development of future atomic clocks at the National Institute of Standards and Technology (NIST) is discussed. The atomic fountain clock called NIST-F1, the primary frequency standard at NIST, is designed to measure the energy splitting of the hyperfine ground states of the /sup 133/Cs atom with a very high degree of accuracy. The next generation of fountain clock is currently being designed at NIST and is in the early stages of testing. One modification to the apparatus will be to cool the drift region to cryogenic temperature, thereby reducing the correction for the black-body radiation frequency shift to a negligible level. An additional modification will be to reduce the atom density during the measurement while increasing the atom throughput in order to reduce the cold-collision frequency shift. Another up-and-coming frequency standard in progress is the Primary Atomic Reference Clock in Space (PARCS) project, which is an atomic-clock mission currently scheduled to fly aboard the International Space Station (ISS) in 2007. The mission involves a laser-cooled cesium atomic clock and a time-transfer system using the Global Positioning System satellites. The microgravity environment aboard the ISS will allow for observation times much longer than feasible on earth. The objectives of the mission are to test gravitational theory and to realize the second with an uncertainty of 1×10/sup -16/ - a factor of 10 better than that achieved on earth.