Hi I believe the “guess” is that all will be met within a year or three.
Bob > On May 29, 2019, at 12:22 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.
