title: Systematic evaluation of an atomic clock at 2 × 10(-18) total uncertainty.
abstract: The pursuit of better atomic clocks has advanced many research areas, providing better quantum state control, new insights in quantum science, tighter limits on fundamental constant variation and improved tests of relativity. The record for the best stability and accuracy is currently held by optical lattice clocks. Here we take an important step towards realizing the full potential of a many-particle clock with a state-of-the-art stable laser. Our (87)Sr optical lattice clock now achieves fractional stability of 2.2 × 10(-16) at 1 s. With this improved stability, we perform a new accuracy evaluation of our clock, reducing many systematic uncertainties that limited our previous measurements, such as those in the lattice ac Stark shift, the atoms' thermal environment and the atomic response to room-temperature blackbody radiation. Our combined measurements have reduced the total uncertainty of the JILA Sr clock to 2.1 × 10(-18) in fractional frequency units.
authors.affiliation: JILA, National Institute of Standards and Technology and University of Colorado, Boulder, Colorado 80309-0440, USA.|Department of Physics, University of Colorado, Boulder, Colorado 80309-0390, USA.
authors.forename: T L
authors.initials: TL
authors.lastname: Nicholson
authors.affiliation: JILA, National Institute of Standards and Technology and University of Colorado, Boulder, Colorado 80309-0440, USA.|Department of Physics, University of Colorado, Boulder, Colorado 80309-0390, USA.
authors.forename: S L
authors.initials: SL
authors.lastname: Campbell
authors.affiliation: JILA, National Institute of Standards and Technology and University of Colorado, Boulder, Colorado 80309-0440, USA.|Department of Physics, University of Colorado, Boulder, Colorado 80309-0390, USA.
authors.forename: R B
authors.initials: RB
authors.lastname: Hutson
authors.affiliation: JILA, National Institute of Standards and Technology and University of Colorado, Boulder, Colorado 80309-0440, USA.|Department of Physics, University of Colorado, Boulder, Colorado 80309-0390, USA.
authors.forename: G E
authors.initials: GE
authors.lastname: Marti
authors.affiliation: JILA, National Institute of Standards and Technology and University of Colorado, Boulder, Colorado 80309-0440, USA.|Department of Physics, University of Colorado, Boulder, Colorado 80309-0390, USA.
authors.forename: B J
authors.initials: BJ
authors.lastname: Bloom
authors.affiliation: JILA, National Institute of Standards and Technology and University of Colorado, Boulder, Colorado 80309-0440, USA.|Department of Physics, University of Colorado, Boulder, Colorado 80309-0390, USA.
authors.forename: R L
authors.initials: RL
authors.lastname: McNally
authors.affiliation: JILA, National Institute of Standards and Technology and University of Colorado, Boulder, Colorado 80309-0440, USA.|Department of Physics, University of Colorado, Boulder, Colorado 80309-0390, USA.
authors.forename: W
authors.identifier: http://orcid.org/0000-0003-2065-2535
authors.initials: W
authors.lastname: Zhang
authors.affiliation: JILA, National Institute of Standards and Technology and University of Colorado, Boulder, Colorado 80309-0440, USA.|Centre for Quantum Technologies, 3 Science Drive 2, Singapore 117543, Singapore.
authors.forename: M D
authors.initials: MD
authors.lastname: Barrett
authors.affiliation: University of Delaware, Newark, Delaware 19716, USA.|Joint Quantum Institute, NIST and the University of Maryland, College Park, Maryland 20899, USA.
authors.forename: M S
authors.initials: MS
authors.lastname: Safronova
authors.affiliation: National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA.
authors.forename: G F
authors.initials: GF
authors.lastname: Strouse
authors.affiliation: National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA.
authors.forename: W L
authors.initials: WL
authors.lastname: Tew
authors.affiliation: JILA, National Institute of Standards and Technology and University of Colorado, Boulder, Colorado 80309-0440, USA.|Department of Physics, University of Colorado, Boulder, Colorado 80309-0390, USA.
authors.forename: J
authors.initials: J
authors.lastname: Ye