title: A 920-kilometer optical fiber link for frequency metrology at the 19th decimal place.
abstract: Optical clocks show unprecedented accuracy, surpassing that of previously available clock systems by more than one order of magnitude. Precise intercomparisons will enable a variety of experiments, including tests of fundamental quantum physics and cosmology and applications in geodesy and navigation. Well-established, satellite-based techniques for microwave dissemination are not adequate to compare optical clocks. Here, we present phase-stabilized distribution of an optical frequency over 920 kilometers of telecommunication fiber. We used two antiparallel fiber links to determine their fractional frequency instability (modified Allan deviation) to 5 × 10(-15) in a 1-second integration time, reaching 10(-18) in less than 1000 seconds. For long integration times τ, the deviation from the expected frequency value has been constrained to within 4 × 10(-19). The link may serve as part of a Europe-wide optical frequency dissemination network.
authors.affiliation: Max-Planck-Institut für Quantenoptik, Garching, Germany. kdp@mpq.mpg.de
authors.forename: K
authors.initials: K
authors.lastname: Predehl
authors.forename: G
authors.initials: G
authors.lastname: Grosche
authors.forename: S M F
authors.initials: SM
authors.lastname: Raupach
authors.forename: S
authors.initials: S
authors.lastname: Droste
authors.forename: O
authors.initials: O
authors.lastname: Terra
authors.forename: J
authors.initials: J
authors.lastname: Alnis
authors.forename: Th
authors.initials: T
authors.lastname: Legero
authors.forename: T W
authors.initials: TW
authors.lastname: Hänsch
authors.forename: Th
authors.initials: T
authors.lastname: Udem
authors.forename: R
authors.initials: R
authors.lastname: Holzwarth
authors.forename: H
authors.initials: H
authors.lastname: Schnatz