title: Frequency ratio of two optical clock transitions in 171Yb+ and constraints on the time variation of fundamental constants.
abstract: Singly ionized ytterbium, with ultranarrow optical clock transitions at 467 and 436 nm, is a convenient system for the realization of optical atomic clocks and tests of present-day variation of fundamental constants. We present the first direct measurement of the frequency ratio of these two clock transitions, without reference to a cesium primary standard, and using the same single ion of 171Yb+. The absolute frequencies of both transitions are also presented, each with a relative standard uncertainty of 6×10(-16). Combining our results with those from other experiments, we report a threefold improvement in the constraint on the time variation of the proton-to-electron mass ratio, μ/μ=0.2(1.1)×10(-16)  yr(-1), along with an improved constraint on time variation of the fine structure constant, α/α=-0.7(2.1)×10(-17)  yr(-1).
authors.affiliation: National Physical Laboratory, Hampton Road, Teddington TW11 0LW, United Kingdom.
authors.forename: R M
authors.initials: RM
authors.lastname: Godun
authors.affiliation: National Physical Laboratory, Hampton Road, Teddington TW11 0LW, United Kingdom.
authors.forename: P B R
authors.initials: PB
authors.lastname: Nisbet-Jones
authors.affiliation: National Physical Laboratory, Hampton Road, Teddington TW11 0LW, United Kingdom and School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT, United Kingdom.
authors.forename: J M
authors.initials: JM
authors.lastname: Jones
authors.affiliation: National Physical Laboratory, Hampton Road, Teddington TW11 0LW, United Kingdom.
authors.forename: S A
authors.initials: SA
authors.lastname: King
authors.affiliation: National Physical Laboratory, Hampton Road, Teddington TW11 0LW, United Kingdom.
authors.forename: L A M
authors.initials: LA
authors.lastname: Johnson
authors.affiliation: National Physical Laboratory, Hampton Road, Teddington TW11 0LW, United Kingdom.
authors.forename: H S
authors.initials: HS
authors.lastname: Margolis
authors.affiliation: National Physical Laboratory, Hampton Road, Teddington TW11 0LW, United Kingdom.
authors.forename: K
authors.initials: K
authors.lastname: Szymaniec
authors.affiliation: National Physical Laboratory, Hampton Road, Teddington TW11 0LW, United Kingdom.
authors.forename: S N
authors.initials: SN
authors.lastname: Lea
authors.affiliation: School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT, United Kingdom.
authors.forename: K
authors.initials: K
authors.lastname: Bongs
authors.affiliation: National Physical Laboratory, Hampton Road, Teddington TW11 0LW, United Kingdom.
authors.forename: P
authors.initials: P
authors.lastname: Gill