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We have demonstrated an atom interferometer with completely separated beams using three 200 nm period transmission gratings. A stretched 10 cm long and 10 μm thick metal foil, was inserted in the interferometer so that separated portions of the atom wave went on opposite sides of the foil. A fringe amplitude of up to 900 cps was observed, which allows us to determine the phase to 15 milliradians in...
Four rubidium fountains have been in continuous operation at USNO for more than 3 years. They contribute to the local timescale and are reported to the BIPM as continuously running clocks — as opposed to secondary standards — the first and only cold-atom clocks so reported. Measurements among individual fountains demonstrate fractional-frequency stability that routinely reaches the low 10∼16s. Intervals...
Four rubidium fountains have been in operation for the past 1.2 years at USNO. Individual fountain performance, applications to timekeeping and to tests of Local Position Invariance are presented.
Performance of the first two operational rubidium fountains at the USNO is presented using relative measurements and comparisons against other timescales. Recent results with four fountains indicate frequency agreement at the 10−15 level and good agreement with the primary frequency standards contributing to TAI.
The U.S. Naval Observatory has an ongoing program to develop atomic fountains for eventual incorporation into the USNO Master Clock. The fountains are being constructed to provide a stable frequency reference which will allow for rapid characterization of drift of masers in our clock ensemble. In support of this goal we are using rubidium to exploit the small cold-collision frequency shift. We report...
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