Thanks, Bruce! That's a copy of that same Science article. I guess that NIST got permission to post it on their website, since they were the sponsor of the study. -- Bill N5BB
On Thu, Jun 4, 2020, at 6:32 PM, Bruce Griffiths wrote: > 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 <[email protected]> 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 -- [email protected] > > To unsubscribe, go to > > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > > and follow the instructions there. > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
