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Intercontinental comparison of optical clocks using very long baseline interferometry
Marco Pizzocaro (INRIM)
Thursday 08/04/2021 @ 11:30, Remote Talk
The seminar will present the results of the first intercontinental comparison of optical clocks using very long baseline interferometry (VLBI). Optical atomic clocks are a candidate for the redefinition of the second and their remote comparison enables fundamental physics experiments such as the chronometric determination of gravitational potential or the search for variations of fundamental constants. While VLBI routinely uses atomic clocks for astronomy and geodetic measurements it can also provide clock comparison when observing well-known radio sources. We exploited this principle to compare two remote optical clocks, using two transportable VLBI antennas with 2.4 m diameter, installed at NICT Koganei in Japan and the INAF Medicina Radio Observatory in Italy, realizing a VLBI node-hub network together with the Kashima large-aperture antenna also in Japan. These antennas implement broadband VLBI observations to improve the signal to noise ratio and compensate for the small antenna size. Using the VLBI link, we compared the strontium optical clock at NICT with the ytterbium optical clock at INRIM in Italy, which is connected to the Medicina Radio Observatory with a phase-stabilised optical fibre link. We show that this system provides higher resolution than standard clock comparison techniques based on satellites. This result opens new opportunities for long-term stable international clock comparisons, with impact to primary metrology and fundamental physics.