title: Direct comparison of a Ca+ single-ion clock against a Sr lattice clock to verify the absolute frequency measurement.
abstract: Optical frequency comparison of the (40)Ca(+) clock transition ν(Ca)((2)S(1/2-)(2D(5/2), 729 nm) against the (87)Sr optical lattice clock transition ν(Sr) ((1)S(0)-(3)P(0), 698 nm) has resulted in a frequency ratio ν(Ca) / ν(Sr) = 0.957 631 202 358 049 9(2 3). The rapid nature of optical comparison allowed the statistical uncertainty of frequency ratio ν(Ca) / ν(Sr) to reach 1 × 10(-15) in 1000s and yielded a value consistent with that calculated from separate absolute frequency measurements of ν(Ca) using the International Atomic Time (TAI) link. The total uncertainty of the frequency ratio using optical comparison (free from microwave link uncertainties) is smaller than that obtained using absolute frequency measurement, demonstrating the advantage of optical frequency evaluation. We note that the absolute frequency of (40)Ca(+) we measure deviates from other published values by more than three times our measurement uncertainty.
authors.affiliation: National Institute of Information and Communications Technology, 4-2-1 Nukui-kitamachi, Koganei, Tokyo 184-8795 Japan. matubara@nict.go.jp
authors.forename: Kensuke
authors.initials: K
authors.lastname: Matsubara
authors.forename: Hidekazu
authors.initials: H
authors.lastname: Hachisu
authors.forename: Ying
authors.initials: Y
authors.lastname: Li
authors.forename: Shigeo
authors.initials: S
authors.lastname: Nagano
authors.forename: Clayton
authors.initials: C
authors.lastname: Locke
authors.forename: Asahiko
authors.initials: A
authors.lastname: Nogami
authors.forename: Masatoshi
authors.initials: M
authors.lastname: Kajita
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Hayasaka
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Ido
authors.forename: Mizuhiko
authors.initials: M
authors.lastname: Hosokawa
mesh_terms: D002118:Calcium / Q000737:chemistry*; D017076:Computer-Aided Design; D004867:Equipment Design; D019544:Equipment Failure Analysis; D006801:Humans; D055096:Optical Devices; D009991:Oscillometry / Q000295:instrumentation* / Q000379:methods*; D013324:Strontium / Q000737:chemistry*; D013997:Time Factors
chemical_list: D002118:Calcium; D013324:Strontium