Comparing Remote Atomic Clocks via VLBI Networks and Fiber Optic Links: the LIFT/MetGeSp Perspective

Abstract

Very Long Baseline Interferometry experiments require an extremely precise synchronization between the atomic clocks keeping the time and frequency standards at radiotelescope observatories. Recently the availability of fiber optic links from a few radio observatories and their national metrological institutes has made the streaming of extremely stable frequency standards via optical atomic clocks possible (even two orders of magnitudes better than Rubidium or Hydrogen maser standards). Firstly, we present the infrastructure of the Italian Link for Frequency and Time (LIFT) and results of the MetGeSp project aimed at finally creating a common clock between two of the antennas of the VLBI Italian Network. Secondly, the results are shown from VLBI experiments in which the rms phase noise was used to accurately compare the synchronicity of atomic clocks located at a few European stations (Medicina, Noto, Yebes, Torun, and Matera). VLBI clock timing proves a valid alternative to satellite-based techniques such as the Global Navigation Satellite System or the Two-Way Satellite Time and Frequency Transfer.