Hi, Dana My understanding is that all criteria should be met, but the list might be refined. Dr. Martin Milton, Director of the BIPM gave a talk on the subject on this years IFCS/EFTF; https://www.youtube.com/watch?v=Qsgl8AHBU7c (redefinition of the second at around 33 minutes, but the whole talk is worth watching).
Ole On Wed, May 29, 2019 at 7:00 PM Dana Whitlow <[email protected]> wrote: > Ole, > > Is it when all 5 conditions are met, or just any one of them? > > Thanks, > > Dana > > > On Wed, May 29, 2019 at 11:00 AM Ole Petter Rønningen < > [email protected]> > wrote: > > > As supporting material; BIPM is considering when a redefinition would be > > appropriate: > > https://www.bipm.org/utils/common/pdf/CGPM-2018/CGPM-2018-Time-2-LD.pdf > > > > And > > https://www.bipm.org/utils/en/pdf/CCTF-strategy-document.pdf annex 1 > (and > > a few other places) > > > > Extract: > > The time for a new definition is right when ... > > > > 1. ... at least three different optical clocks (either in different > > laboratories, or of different species) have demonstrated validated > > uncertainties of about two orders of magnitude better than the best Cs > > atomic clocks at that time. > > > > 2. ... at least three independent measurements of at least one optical > > clock of milestone 1 were compared in different institutes (e.g. Df/f < > 5 x > > 10-18) either by transportable clocks, advanced links, or frequency ratio > > closures. > > > > 3. ... there are three independent measurements of the optical frequency > > standards listed in milestone 1 with three independent Cs primary clocks, > > where the measurements are limited essentially by the uncertainty of > these > > Cs fountain > > clocks (e.g. Df/f< 3 x 10-16). > > > > 4. ... optical clocks (secondary representations of the second) > contribute > > regularly to TAI. > > > > 5. ... optical frequency ratios between a few (at least 5) other optical > > frequency standards have been performed; each ratio measured at least > twice > > by independent laboratories and agreement was found (with e.g. Df/f < > > 5x10-18). > > > > Br, > > Ole > > > > > 29. mai 2019 kl. 15:16 skrev Attila Kinali <[email protected]>: > > > > > > On Tue, 28 May 2019 22:56:35 +0200 > > > Mike Cook <[email protected]> wrote: > > > > > >> a. There is no need for a new definition. > > > > > > There is. Current optical clocks deliver a lower uncertainty than > > > Cs fountain clocks. Ie the reference we have is less precise than > > > the measurement tools we have. Hence a redefinition of the second > > > is needed. > > > > > >> b. Any new definition would have to be realizable and easily > > verifiable. > > > > > > That's one of the main concerns and this is also the main reason why > > > nobody is actively pursuing a redefinition just yet. But there are > people > > > out there who are already working on this topic and gathering all the > > > requirements to a successful redefinition of the second. My guess, > > > based on the current speed of things, is that we will have a new > > > definition of the second within 10-15 years. > > > > > >> c. The first commercial cesium clocks were available in 1956, but the > > second did not get redefined until 1967. There is no rush. > > > > > > Which caesium beam standards were available in 1956? AFAIK the first > one > > > was the HP5061 and that came much later. Essen and Parry built their > > > clock in the 1950s and published the results in 1955. The picture of > the > > > beam tube is only a small fraction of the clock itself. There are > > multiple > > > racks full of RF equipment not shown. I would be very surprised if > there > > > was any company that was able to commercialize this contraption within > > > only a year. Even in this large size. > > > > > >> I believe that commercial optical clocks are available but: > > > > > > No. As far as I am aware of, there are no commercial optical clocks > > > available. There are a few optically pumped microwave clocks out there > > > (e.g. by Oscilloquartz) and even cold atom clocks (by Muquans and SDI) > > > but no optical clocks. > > > > > > The main problem with optical clocks is the frequency division of the > > > optical signal down to something that can be used in electronics. > > > This is usually done using an optical comb. But the commercially > > > available ones are big, and according to Michael Wouters also quite > > > expensive. There are efforts to use non-linear optical rings to > > > generate these combs, but there is no commercial version available > > > yet (it's a very new technique, which has been around just a few years) > > > > > > The closest I know to a commercial product is what NIST reported > > > in Optica just a few days ago[1] (based on two-photon absorption > > > in a Rb vapor cell and using two optical combs to divide the > > > 778nm down to 22GHz). > > > > > >> d. There are too many flavors of optical clocks around on lab benches. > > So despite their increased precision and stability which flavor would get > > the vote? > > > > > > This is another issue. Of course, a redefinition will use one atomic > > species > > > only (with the others probably becoming secondary definitions). So far > > > the jury is still out which of the atoms and which method is the best > > one. > > > As there are not yet enough optical clocks out there, we don't have > > enough > > > data to decide yet. And it doesn't help that an optical atomic clock > > takes > > > several years and a quite large team to build. > > > > > > Attila Kinali > > > > > > [1] "Architecture for the photonic integration of an optical atomic > > clock", > > > by Newman et al., 2019 > > > https://doi.org/10.1364/OPTICA.6.000680 > > > -- > > > It is upon moral qualities that a society is ultimately founded. All > > > the prosperity and technological sophistication in the world is of no > > > use without that foundation. > > > -- Miss Matheson, The Diamond Age, Neal Stephenson > > > > > > _______________________________________________ > > > 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. > _______________________________________________ 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.
