title: Frequency comparison of two high-accuracy Al+ optical clocks.
abstract: We have constructed an optical clock with a fractional frequency inaccuracy of 8.6x10{-18}, based on quantum logic spectroscopy of an Al+ ion. A simultaneously trapped Mg+ ion serves to sympathetically laser cool the Al+ ion and detect its quantum state. The frequency of the {1}S{0}<-->{3}P{0} clock transition is compared to that of a previously constructed Al+ optical clock with a statistical measurement uncertainty of 7.0x10{-18}. The two clocks exhibit a relative stability of 2.8x10{-15}tau{-1/2}, and a fractional frequency difference of -1.8x10{-17}, consistent with the accuracy limit of the older clock.
authors.affiliation: Time and Frequency Division, National Institute of Standards and Technology, Boulder, Colorado 80305, USA. chinwen@nist.gov
authors.forename: C W
authors.initials: CW
authors.lastname: Chou
authors.forename: D B
authors.initials: DB
authors.lastname: Hume
authors.forename: J C J
authors.initials: JC
authors.lastname: Koelemeij
authors.forename: D J
authors.initials: DJ
authors.lastname: Wineland
authors.forename: T
authors.initials: T
authors.lastname: Rosenband