https://tf.nist.gov/general/pdf/3093.pdf is likely more accessible than the sciencemag link
Bruce > On 05 June 2020 at 11:15 Bill Byrom <t...@radio.sent.com> wrote: > > > This was published in the 22 May 2020 issue of Science (AAAS journal). For > AAAS members, the direct link is: > https://science.sciencemag.org/content/368/6493/889 > > They make use of a fiber-based OFC (optical frequency comb) and > state-of-the-art photodetectors to transfer optical clock stability to a 10 > GHz microwave signal. This downconversion from optical to microwave was done > with an error of no more than 10-19 (1 x 10 ^-19). The best available optical > clock stability is around 10-18 (1 x 10^-18) at a couple of hundred seconds > averaging time. > > This specific experiment compared two independent Yb (Ytterbium) optical > lattice clocks running at about 259 THz. One Yb clock drove a 208 MHz comb > generator, while the other Yb clock drove a 156 MHz comb generator. Then: > 208 MHz x 48th harmonic = 9.984 GHz > 156 MHz x 64th harmonic = 9.984 GHz > The phase between these 9.984 GHz signals was compared in a mixer phase > detector. The fractional frequency instability observed was 10-16 (1 x > 10^-16) over a 1 second interval. The frequencies I listed above are > approximate -- they actually measured a 1.5 MHz beat note between the ~10 GHz > signals. This allowed them to achieve a relative timing error of 900 > attoseconds (rms). > > The optical phase measurements between the two Yb clocks at 259 THz indicated > a frequency offset (Yb1 - Yb2) of 0.0000064 Hz, and the microwave ~10 GHz > comparison was consistent with that offset (2.5 +/- 0.6) x 10-20 (10^-20). > > The abstract is: > > Optical atomic clocks are poised to redefine the Système International (SI) > > second, thanks to stability > > and accuracy more than 100 times better than the current microwave atomic > > clock standard. However, > > the best optical clocks have not seen their performance transferred to the > > electronic domain, where > > radar, navigation, communications, and fundamental research rely on less > > stable microwave sources. > > By comparing two independent optical-to-electronic signal generators, we > > demonstrate a 10-gigahertz > > microwave signal with phase that exactly tracks that of the optical clock > > phase from which it is derived, > > yielding an absolute fractional frequency instability of 1 × 10−18 in the > > electronic domain. Such faithful > > reproduction of the optical clock phase expands the opportunities for > > optical clocks both technologically > > and scientifically for time dissemination, navigation, and long-baseline > > interferometric imaging. > > I have a Science subscription and can read this paper, but I can't distribute > it here. > > You can also see discussion of this achievement by NIST (with assistance by > the University of Virginia) at Physics World: > https://physicsworld.com/a/microwave-timing-signals-get-hundredfold-boost-in-stability/ > > You may need to request a free account at Physics World to read this article. > > -- > Bill Byrom N5BB > > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
