Real-time geopotentiometry with synchronously linked optical lattice clocks

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.

25 pages, 4 figures, published online 15 August 2016 in Nature Photonics

References in corpus (6)

• Sr lattice clock at 1x10^{-16} fractional uncertainty by remote optical evaluation with a Ca clock
• A New Method for Gravitational Wave Detection with Atomic Sensors
• Coherent optical frequency transfer at 5e-19 over a doubled 642 km fiber link
• A transportable strontium optical lattice clock
• Carrier-phase Two-Way Satellite Frequency Transfer over a Very Long Baseline
• Strategies for reducing the light shift in atomic clocks

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• All-polarization-maintaining, single-port Er:fiber comb for high-stability comparison of optical lattice clocks
• Precise determination of the isotope shift of ${}^{88}$Sr - ${}^{87}$Sr optical lattice clock by sharing perturbations