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

Wed May 29 17:25:25 UTC 2019

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 <k8yumdoober at gmail.com> 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 <
> 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.
> >
> _______________________________________________
> 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.
>