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      Real-time geopotentiometry with synchronously linked optical lattice clocks

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          Abstract

          According to the Einstein's theory of relativity, the passage of time changes in a gravitational field. On earth, raising a clock by one centimetre increases its tick rate by 1.1 parts in 10\(^{18}\), enabling optical clocks to perform precision geodesy. Here, we demonstrate geopotentiometry by determining the height difference of master and slave clocks separated by 15 km with uncertainty of 5 cm. The subharmonic of the master clock is delivered through a telecom fibre to phase-lock and synchronously interrogate the slave clock. This protocol rejects laser noise in the comparison of two clocks, which improves the stability of measuring the gravitational red shift. Such phase-coherently operated clocks facilitate proposals for linking clocks and interferometers. Over half a year, 11 measurements determine the fractional frequency difference between the two clocks to be \(1,652.9(5.9)\times 10^{-18}\), or a height difference of 1,516(5) cm, consistent with an independent measurement by levelling and gravimetry. Our system is as a building block of an internet of clocks, consisting of a master and a number of slave clocks, which will provide "quantum benchmarks" that are height references with dynamic response.

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          Author and article information

          Journal
          2016-08-26
          Article
          10.1038/nphoton.2016.159
          1608.07650

          http://arxiv.org/licenses/nonexclusive-distrib/1.0/

          Custom metadata
          25 pages, 4 figures, published online 15 August 2016 in Nature Photonics
          physics.atom-ph physics.geo-ph

          Geophysics, Atomic & Molecular physics

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