We report in this letter the outstanding frequency stability performances of an autonomous cryogenique sapphire oscillator presenting a flicker frequency noise floor below 2e-16 near 1,000 s of integration time and a long term Allan Deviation (ADEV) limited by a random walk process of 1e-18/sqr(tau). The frequency stability qualification at this level called for the implementation of sophisticated instrumentation associated with ultra-stable frequency references and ad hoq averaging and correlation methods.
@article{arxiv.2210.06059,
title = {A Cryogenic Sapphire Resonator Oscillator with 1e-16 mid-term fractional frequency stability},
author = {Christophe Fluhr and Benoit Dubois and Claudio E. Calosso and Francois Vernotte and Enrico Rubiola and Vincent Giordano},
journal= {arXiv preprint arXiv:2210.06059},
year = {2023}
}