[time-nuts] Updating the unit of,time: the second.

Wed May 29 16:22:04 UTC 2019

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 <opronningen at gmail.com>
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 <attila at kinali.ch>:
> >
> > On Tue, 28 May 2019 22:56:35 +0200
> > Mike Cook <michael.cook at sfr.fr> 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 -- time-nuts at 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 at lists.febo.com
> To unsubscribe, go to
> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
> and follow the instructions there.
>