Geopotential measurements with synchronously linked optical lattice clocks
Geopotential measurements with synchronously linked optical lattice clocks
Nature Photonics (2016) doi:10.1038/nphoton.2016.159
Received 10 March 2016 Accepted 11 July 2016 Published online 15 August 2016
According to Einstein's theory of relativity, the passage of time changes in a gravitational field1, 2. On Earth, raising a clock by 1 cm increases its apparent tick rate by 1.1 parts in 1018, allowing chronometric levelling3 through comparison of optical clocks1, 4, 5. Here, we demonstrate such geopotential measurements by determining the height difference of master and slave clocks separated by 15 km with an uncertainty of 5 cm. A subharmonic of the master clock laser is delivered through a telecom fibre6 to synchronously operate7 the distant clocks. Clocks operated under such phase coherence reject clock laser noise and facilitate proposals for linking clocks8, 9 and interferometers10. Taken over half a year, 11 measurements determine the fractional frequency difference between the two clocks to be 1,652.9(5.9) × 10−18, consistent with an independent measurement by levelling and gravimetry11. Our system demonstrates a building block for an internet of clocks, which may constitute ‘quantum benchmarks’, serving as height references with dynamic responses.
http://www.nature.com/nphoton/journal/vaop/ncurrent/full/nphoton.2016.159.html
