title: A clock directly linking time to a particle's mass.
abstract: Historically, time measurements have been based on oscillation frequencies in systems of particles, from the motion of celestial bodies to atomic transitions. Relativity and quantum mechanics show that even a single particle of mass m determines a Compton frequency ω(0) = mc(2)/[formula: see text] where c is the speed of light and [formula: see text] is Planck's constant h divided by 2π. A clock referenced to ω(0) would enable high-precision mass measurements and a fundamental definition of the second. We demonstrate such a clock using an optical frequency comb to self-reference a Ramsey-Bordé atom interferometer and synchronize an oscillator at a subharmonic of ω(0.) This directly demonstrates the connection between time and mass. It allows measurement of microscopic masses with 4 × 10(-9) accuracy in the proposed revision to SI units. Together with the Avogadro project, it yields calibrated kilograms.
authors.affiliation: Department of Physics, University of California-Berkeley, CA 94720, USA.
authors.forename: Shau-Yu
authors.initials: SY
authors.lastname: Lan
authors.forename: Pei-Chen
authors.initials: PC
authors.lastname: Kuan
authors.forename: Brian
authors.initials: B
authors.lastname: Estey
authors.forename: Damon
authors.initials: D
authors.lastname: English
authors.forename: Justin M
authors.initials: JM
authors.lastname: Brown
authors.forename: Michael A
authors.initials: MA
authors.lastname: Hohensee
authors.forename: Holger
authors.initials: H
authors.lastname: Müller