High-accuracy microwave and optical frequency standards using laser-cooled Hg+ ions

摘要

We discuss frequency standards based on laser-cooled Hg-199(+) ions confined in cryogenic rf (Paul) traps. In one experiment, the frequency of a microwave source is servoed to the ions' ground-state hyperfine transition at 40.5 GHz. For seven ions and a Ramsey free precession time of 100 s, the fractional frequency stability is 3.3 (2) x 10(-13) tau(-1/2) for measurement times tau < 2 h. The ground-state hyperfine interval is measured to be 40507347996.84159(20)(41) Hz, where the first number in parentheses is the uncertainty due to statistics and systematic effects, and the second is the uncertainty in the frequency of the time scale to which the standard is compared. In a second experiment under development, a strong-binding cryogenic trap will confine a single ion used for an optical frequency standard based on a narrow electric quadrupole transition at 282 nm. The bandwidth of the laser used to drive this transition is less than 10 Hz at 563 nm. [References: 27]