2016/08/15 by Tetsushi Takano, T. Takano, Masao Takamoto +8 · 2 citations
Medicine · Physics and Astronomy · #Advanced Frequency and Time Standards #Atomic clock #Cardiovascular Syncope and Autonomic Disorders #Cold Atom Physics and Bose-Einstein Condensates #Geodesy #Geology #Gravitational wave #Optics #Physics #Quantum mechanics #physics.atom-ph #physics.geo-ph
paper · pdf · doi:10.1038/nphoton.2016.159
25 pages, 4 figures, published online 15 August 2016 in Nature Photonics
openalex publication_date 2016/08/15 · arxiv created 2016/08/27 · arxiv updated 2016/08/30 · openalex created_date 2016/09/16 · openalex updated_date 2026/08/05
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 1018, 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)× 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.