The USNO rubidium fountains

[摘要] Four rubidium fountains at the U.S. Naval Observatory (USNO) have been in operation for 4.5 years. Each fountain has demonstrated periods of stability marked by Total or Theo deviation below 10-16Occasional frequency changes, on order of 1.5 times per year per fountain, introduce deviations from white-frequency noise behavior. Averaged together, the four fountains form an ensemble with a white-frequency noise level of 10-13and excellent long-term stability as compared to the primary frequency standards contributing to TAI. Progress on using the clocks at USNO for improving limits on coupling of fundamental constants to gravity by measuring the universality of the gravitational redshift for different types of clocks is discussed.

[发布机构] United States Naval Observatory, 3450 Massachusetts Ave. NW, Washington; DC; 20392, United States^1

[关键词] Frequency changes;Frequency noise;Fundamental constants;Gravitational redshift;Long term stability;Primary frequency standard;U.s. naval observatories