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

[Tony Finch]

Attila Kinali  wrote:
> Mike Cook  wrote:
>
> > 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?

The Atomichron, I think:

http://ieeemilestones.ethw.org/images/8/8d/Forman_Proc_IEEE_1985.pdf

Tony.
-- 
f.anthony.n.finchhttp://dotat.at/
Fair Isle: Southwest 5 or 6, becoming variable 4 later. Moderate or rough.
Showers, rain later. Good, occasionally poor later.

___
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe, go to 
http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
and follow the instructions there.

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

[Tom Van Baak]

Mike, Attila, Rick,

> Which caesium beam standards were available in 1956?

The Atomichron, made by the National Company. This was the first 
commercial cesium standard; about 50 were made. Attila, you saw one at 
my house when you visited last year. It's about 7 feet tall. The one I 
have was used by NBS(NIST), then made its way to a remote cabin in 
Minnesota for a couple decades, then to a garage in Minneapolis, where I 
bought it and drove it to Seattle. Atomichron photos here [1].


The hp 5060 and 5061 came much later.

> 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


Correct. Better views of Essen's cesium clock and laboratory here [2]. 
Note also the Atomichron in the background of figure 6.


Since you are interested in the history of atomic clocks, especially 
cesium beam clocks, I highly recommend these papers:


http://geodesy.unr.edu/hanspeterplag/library/geodesy/time/met5_3_S01.pdf
"History of early atomic clocks"
Norman F Ramsey

http://geodesy.unr.edu/hanspeterplag/library/geodesy/time/met5_3_S02.pdf
"Essen and the National Physical Laboratory’s atomic clock"
Dale Henderson

http://geodesy.unr.edu/hanspeterplag/library/geodesy/time/met5_3_S04.pdf
"Atomic time-keeping from 1955 to the present"
Bernard Guinot, Elisa Felicitas Arias

http://geodesy.unr.edu/hanspeterplag/library/geodesy/time/met5_3_s05.pdf
"The classical caesium beam frequency standard: fifty years later"
Jacques Vanier, Claude Audoin

http://geodesy.unr.edu/hanspeterplag/library/geodesy/time/met5_3_S10.pdf
"Fifty years of commercial caesium clocks"
Leonard S Cutler

The above come from:

https://iopscience.iop.org/issue/0026-1394/42/3
Special issue of Metrologia: “Special issue: fifty years of atomic 
time-keeping: 1955 to 2005”,

Volume 42, Number 3, June 2005.

See also:

https://ieee-uffc.org/about-us/history/uffc-s-history/history-of-atomic-frequency-standards-a-trip-through-20th-century-physics/
"History of Atomic Frequency Standards: A Trip Through 20th Century Physics"
Arthur O. McCoubrey

https://ieee-uffc.org/about-us/history/uffc-s-history/atomichron/
"Atomichron: The Atomic Clock from Concept to Commercial Product"
Paul Forman

https://tycho.usno.navy.mil/ptti/1985papers/Vol%2017_01.pdf
The First Atomic Clock Program: NBS, 1947-1954
Paul Forman

A fine collection of clear photos and historical PDF here:



And finally,

https://nvlpubs.nist.gov/nistpubs/jres/122/jres.122.029.pdf
also found here: https://tf.nist.gov/general/pdf/2907.pdf
or here: https://tf.nist.gov/general/pdf/2917.pdf
"A Historical Review of U.S. Contributions to the Atomic Redefinition of 
the SI Second in 1967"

Michael A. Lombardi

/tvb

[1] http://www.leapsecond.com/museum/nc2001/

[2] 
https://www.researchgate.net/publication/320878080_Two_clocks_that_changed_the_world_The_birth_of_atomic_timekeeping



___
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe, go to 
http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
and follow the instructions there.

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

[jimlux]

On 6/3/19 8:52 AM, Richard (Rick) Karlquist wrote:






FWIW, there is a nice article in IEEE Spectrum, Oct. 2014, page 42 on
OLC's that starts out by showing the 1956 (non-commerical) clock by
Parry and Essen.  It has a tutorial on OLC's and a history of the
second.  The author is Prof. Lodewyck from France who actually
builds these things.  Highty recommended, even though now 5 years out
of date.




https://ieeexplore.ieee.org/document/6905489



___
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe, go to 
http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
and follow the instructions there.

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

[Richard (Rick) Karlquist]

On 5/29/2019 6:16 AM, Attila Kinali wrote:

On Tue, 28 May 2019 22:56:35 +0200
Mike Cook  wrote:





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.


Before the HP5061 was the HP5060, which used CBT's made by Varian in the
early 60's.  The old Varian factory site is just about next door to the 
present 5071 production line in MA by a strange coincidence.  Back to

the future.

FWIW, there is a nice article in IEEE Spectrum, Oct. 2014, page 42 on
OLC's that starts out by showing the 1956 (non-commerical) clock by
Parry and Essen.  It has a tutorial on OLC's and a history of the
second.  The author is Prof. Lodewyck from France who actually
builds these things.  Highty recommended, even though now 5 years out
of date.

Rick N6RK

___
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe, go to 
http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
and follow the instructions there.

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

[Bob kb8tq]

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  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 
> 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 :
>>> 
>>> On Tue, 28 May 2019 22:56:35 +0200
>>> Mike Cook  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
>> 

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

[Ole Petter Ronningen]

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  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 <
> opronnin...@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 :
> > >
> > > On Tue, 28 May 2019 22:56:35 +0200
> > > Mike Cook  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 

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

[Dana Whitlow]

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 
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 :
> >
> > On Tue, 28 May 2019 22:56:35 +0200
> > Mike Cook  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
> > 

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

[Ole Petter Rønningen]

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 :
> 
> On Tue, 28 May 2019 22:56:35 +0200
> Mike Cook  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
> 
> ___

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

[Attila Kinali]

On Tue, 28 May 2019 22:56:35 +0200
Mike Cook  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@lists.febo.com
To unsubscribe, go to 
http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
and follow the instructions there.

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

[Mike Cook]

> Le 27 mai 2019 à 11:13, Dave B via time-nuts  a 
> écrit :
> 
> Hi.
> 
> This from the recent ShortWave Radiogram broadcast, may be of interest.
> 
> ~ ~ ~
> 
> (Snipped stuff about other SI units undergoing a revamp...)
> 
> Scientists now have their sights set on updating the unit of
> time: the second.
> 
> Currently, the second is defined by atomic clocks made of cesium
> atoms. Those atoms absorb a certain frequency of light. The
> wiggling of the light's electromagnetic waves functions like the
> pendulum on a grandfather clock, rhythmically keeping time. One
> second is defined as 9,192,631,770 oscillations of the light.
> 
> But a new generation of atomic clocks, known as optical atomic
> clocks, outdo the cesium clocks. "Their performance is a lot
> better than what currently defines the second," says physicist
> Andrew Ludlow of the National Institute of Standards and
> Technology in Boulder, Colo. Because those optical atomic clocks
> operate at a higher frequency, their "ticks" are more closely
> spaced, making them about 100 times more precise than cesium
> clocks.
> 
> Ideally, the length of a second should be defined using the most
> precise timepieces available. A switch might happen in the late
> 2020s, Ludlow says.

I disagree with this.

a. There is no need for a new definition.
b. Any new definition would have to be realizable and easily verifiable. 
c. The first commercial cesium clocks were available in 1956, but the second 
did not get redefined until 1967.  There is no rush.
I believe that commercial optical clocks are available but:
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?

So I predict that that will be no change in the definition in the next 20 years 
and chip scale optical clocks will be available before five years hence.


> 
> The change to the kilogram's definition was carefully
> orchestrated so that it wouldn't affect normal people: A kilogram
> of flour still makes the same number of biscuits. Any change to
> the second will be similarly coordinated.
> 
> So, sorry, there'll be no chance to squeeze any extra seconds
> into a day.
> 
> https://www.sciencenews.org/article/kilogram-just-got-revamp-unit-time-might-be-next
> 
> ~ ~ ~
> 
> So, perhaps a host of surplus cesium clocks on the market at some point?
> 
> 73
> 
> Dave B G0WBX.
> 
> -- 
> Created on and sent from a Unix like PC running and using free and open 
> source software:
> 
> 
> ___
> time-nuts mailing list -- time-nuts@lists.febo.com
> To unsubscribe, go to 
> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
> and follow the instructions there.

"Ceux qui sont prêts à abandonner une liberté essentielle pour obtenir une 
petite et provisoire sécurité, ne méritent ni liberté ni sécurité."
Benjimin Franklin


___
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe, go to 
http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
and follow the instructions there.

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

[jimlux]

On 5/28/19 2:12 AM, Attila Kinali wrote:

On Tue, 28 May 2019 03:06:12 +0100





Another way to look at it is, before you reach the point where the
redefinition of the kg change becomes visible, other errors like
buoyancy of air will introduce errors that are orders of magnitude
largers (uncorrected the buoyancy induced uncertainty is IIRC in the
a few ppm range, corrected its induced uncertainty goes to 1e-8).
So, unless you are doing your weight measurements in vacuum, there is
no need to care about the change of definition of kg.



Air is about 1mg/cc, so your measured mass is off by 1000 ppm if you're 
measuring water (depending on how much air your vessel displaces).  If 
you're weighing lumps of lead (11.3 g/cc), then only 100ppm error.





___
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe, go to 
http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
and follow the instructions there.

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

[Attila Kinali]

On Tue, 28 May 2019 03:06:12 +0100
"Dr. David Kirkby"  wrote:

> I notice a lot of 1 kg weights on eBay, so perhaps the same will happen
> with Cs clocks!

This is rather unlikely. For one, Cs beam standards have a very limited
life span. For an other I am pretty sure that the surge of kg weight
standards on ebay is due to their manufacturing becoming cheap rather
than the kg definition changing. Most of these standards are M1 or M2
anyways (or in other words, they are accurate to 50ppm or 160ppm
respectively [1]), which is way more than the slight change in the 
definition of the kg. 

Another way to look at it is, before you reach the point where the
redefinition of the kg change becomes visible, other errors like
buoyancy of air will introduce errors that are orders of magnitude
largers (uncorrected the buoyancy induced uncertainty is IIRC in the
a few ppm range, corrected its induced uncertainty goes to 1e-8).
So, unless you are doing your weight measurements in vacuum, there is
no need to care about the change of definition of kg.

If we look at frequency standards, then using a simple L1-only GPSDO
brings us to better than 1e-10 for τ > 1s. If you do PPP frequency
transfer as Ole did, you get to 1e-11 for τ > 1s and down to 1e-14
for τ > 1000s. And all that with a very moderate budget. Why spend
thousands of € for a surplus Cs beam that will be out of Cs fumes in 
5-10 years, when I can build a similar quality standard for a fraction
of the cost that is probably going to work for decades to come?

Attila Kinali

[1] OIML R111-1
https://www.oiml.org/en/files/pdf_r/r111-1-e04.pdf
-- 
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@lists.febo.com
To unsubscribe, go to 
http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
and follow the instructions there.

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

[Dr. David Kirkby]

On Mon, 27 May 2019 at 11:20, Dave B via time-nuts 
wrote:

>
>
> https://www.sciencenews.org/article/kilogram-just-got-revamp-unit-time-might-be-next
>
> ~ ~ ~
>
> So, perhaps a host of surplus cesium clocks on the market at some point?
>
> 73
>
> Dave B G0WBX.


I notice a lot of 1 kg weights on eBay, so perhaps the same will happen
with Cs clocks!

I wonder what fraction of users of cesium clocks are using them because a
second is defined the way it currently is? I can’t imagine there will be
lots put on the used market, but it would be nice if there were.

Dave

> --
Dr David Kirkby Ph.D C.Eng MIET
Kirkby Microwave Ltd
Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, CHELMSFORD,
Essex, CM3 6DT, United Kingdom.
Registered in England and Wales as company number 08914892
https://www.kirkbymicrowave.co.uk/
Tel 01621-680100 / +44 1621-680100
___
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe, go to 
http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
and follow the instructions there.

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

[Mark Spencer]

Just as a side note..  I have looked at the propagation of DTV pilot carriers 
(as part of an "over the horizon" VHF radio propagation experiment) and the 
Doppler shifted carriers due to reflections from air craft were typically 
detected separately along with the "over the horizon" pilot carrier (which was 
essentially always present.)  It never occurred to me to look for movement of 
the transmitter.

Sorry for the bandwidth.

Mark Spencer

m...@alignedsolutions.com
604 762 4099

> On May 27, 2019, at 12:38 PM, Dana Whitlow  wrote:
> 
> Well, I once had a nutty idea which was to detect earthquakes by looking
> for the phase
> variation of DTV station pilot carriers due to seismic waves propagating
> around, thereby
> changing the physical distance between transmitter and receiver in a cyclic
> manner
> until the 'quake calmed down.   Doing so would require that the phase
> stability of both
> transmitter and receiver, expressed as length units, be within a fairly
> small fraction of
> an inch.
> 
> I've since figured out that even with a Rb at both ends, this would not
> work out- something
> more like an H-maser would be required.  And one other thing- I had
> completely
> forgotten about Doppler-shifted reflections off aircraft, which often fall
> right in the frequency
> range of seismic waves and persist for durations similar to those of
> earthquakes.  But that's
> what got me interested in time-nuttery.  I still intend to do the
> experiment, just to see what I
> can learn about what other factors might exist which cause propagation
> phase variations.
> 
> Dana
> 
> 
> On Mon, May 27, 2019 at 11:27 AM Bob Albert via time-nuts <
> time-nuts@lists.febo.com> wrote:
> 
>> Well I have enjoyed time and frequency measurement for many years.  I
>> have no equipment (nor do I expect to get any) that can tell the difference
>> between the current second and the proposed standard.  And at one point I
>> asked if there was a limit on the smallest time interval that could be
>> discerned.
>> I do remember being impressed with the Collins gear in the 1950s, and
>> wanting one of those 7 foot racks of time standards made by General Radio,
>> the one with the big clock on top.
>> As the years passed I obtained more and more accurate frequency
> 

___
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe, go to 
http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
and follow the instructions there.

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

[Dana Whitlow]

Well, I once had a nutty idea which was to detect earthquakes by looking
for the phase
variation of DTV station pilot carriers due to seismic waves propagating
around, thereby
changing the physical distance between transmitter and receiver in a cyclic
manner
until the 'quake calmed down.   Doing so would require that the phase
stability of both
transmitter and receiver, expressed as length units, be within a fairly
small fraction of
an inch.

I've since figured out that even with a Rb at both ends, this would not
work out- something
more like an H-maser would be required.  And one other thing- I had
completely
forgotten about Doppler-shifted reflections off aircraft, which often fall
right in the frequency
range of seismic waves and persist for durations similar to those of
earthquakes.  But that's
what got me interested in time-nuttery.  I still intend to do the
experiment, just to see what I
can learn about what other factors might exist which cause propagation
phase variations.

Dana


On Mon, May 27, 2019 at 11:27 AM Bob Albert via time-nuts <
time-nuts@lists.febo.com> wrote:

>  Well I have enjoyed time and frequency measurement for many years.  I
> have no equipment (nor do I expect to get any) that can tell the difference
> between the current second and the proposed standard.  And at one point I
> asked if there was a limit on the smallest time interval that could be
> discerned.
> I do remember being impressed with the Collins gear in the 1950s, and
> wanting one of those 7 foot racks of time standards made by General Radio,
> the one with the big clock on top.
> As the years passed I obtained more and more accurate frequency
> measurement equipment, including a home made heterodyne frequency meter
> that outdid the Collins radios.  Then the lousy radio propagation ended my
> dependence on WWV and I luckily obtained a rubidium oscillator.
> But that's about as far as I want to go.  My HP 8657B resolves 1 Hz at
> more than 2 GHz and it can be set to within a very small error with respect
> to the rubidium standard.  At this point I see no reason to improve my time
> and frequency measurement accuracy.
> Of course it can be an end in itself, hence the name Time Nuts.  So I
> propose the question, how many out there have interest in this topic for
> academic and psychological reasons, and how many actually have a concrete
> reason to be this precise?  One part per billion isn't a lot.  And some
> systems require iron clad synchronism such as space exploration and long
> range communication.  But the average tinkerer probably doesn't need it.
> Bob
> On Monday, May 27, 2019, 3:20:24 AM PDT, Dave B via time-nuts <
> time-nuts@lists.febo.com> wrote:
>
>  Hi.
>
> This from the recent ShortWave Radiogram broadcast, may be of interest.
>
> ~ ~ ~
>
> (Snipped stuff about other SI units undergoing a revamp...)
>
> Scientists now have their sights set on updating the unit of
> time: the second.
>
> Currently, the second is defined by atomic clocks made of cesium
> atoms. Those atoms absorb a certain frequency of light. The
> wiggling of the light's electromagnetic waves functions like the
> pendulum on a grandfather clock, rhythmically keeping time. One
> second is defined as 9,192,631,770 oscillations of the light.
>
> But a new generation of atomic clocks, known as optical atomic
> clocks, outdo the cesium clocks. "Their performance is a lot
> better than what currently defines the second," says physicist
> Andrew Ludlow of the National Institute of Standards and
> Technology in Boulder, Colo. Because those optical atomic clocks
> operate at a higher frequency, their "ticks" are more closely
> spaced, making them about 100 times more precise than cesium
> clocks.
>
> Ideally, the length of a second should be defined using the most
> precise timepieces available. A switch might happen in the late
> 2020s, Ludlow says.
>
> The change to the kilogram's definition was carefully
> orchestrated so that it wouldn't affect normal people: A kilogram
> of flour still makes the same number of biscuits. Any change to
> the second will be similarly coordinated.
>
> So, sorry, there'll be no chance to squeeze any extra seconds
> into a day.
>
>
> https://www.sciencenews.org/article/kilogram-just-got-revamp-unit-time-might-be-next
>
> ~ ~ ~
>
> So, perhaps a host of surplus cesium clocks on the market at some point?
>
> 73
>
> Dave B G0WBX.
>
> --
> Created on and sent from a Unix like PC running and using free and open
> source software:
>
>
> ___
> time-nuts mailing list -- time-nuts@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@lists.febo.com
> To unsubscribe, go to
> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
> and follow the instructions there.
>

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

[Bob Albert via time-nuts]

 Well I have enjoyed time and frequency measurement for many years.  I have no 
equipment (nor do I expect to get any) that can tell the difference between the 
current second and the proposed standard.  And at one point I asked if there 
was a limit on the smallest time interval that could be discerned.
I do remember being impressed with the Collins gear in the 1950s, and wanting 
one of those 7 foot racks of time standards made by General Radio, the one with 
the big clock on top.
As the years passed I obtained more and more accurate frequency measurement 
equipment, including a home made heterodyne frequency meter that outdid the 
Collins radios.  Then the lousy radio propagation ended my dependence on WWV 
and I luckily obtained a rubidium oscillator.
But that's about as far as I want to go.  My HP 8657B resolves 1 Hz at more 
than 2 GHz and it can be set to within a very small error with respect to the 
rubidium standard.  At this point I see no reason to improve my time and 
frequency measurement accuracy.
Of course it can be an end in itself, hence the name Time Nuts.  So I propose 
the question, how many out there have interest in this topic for academic and 
psychological reasons, and how many actually have a concrete reason to be this 
precise?  One part per billion isn't a lot.  And some systems require iron clad 
synchronism such as space exploration and long range communication.  But the 
average tinkerer probably doesn't need it.
Bob
On Monday, May 27, 2019, 3:20:24 AM PDT, Dave B via time-nuts 
 wrote:  
 
 Hi.

This from the recent ShortWave Radiogram broadcast, may be of interest.

~ ~ ~

(Snipped stuff about other SI units undergoing a revamp...)

Scientists now have their sights set on updating the unit of
time: the second.

Currently, the second is defined by atomic clocks made of cesium
atoms. Those atoms absorb a certain frequency of light. The
wiggling of the light's electromagnetic waves functions like the
pendulum on a grandfather clock, rhythmically keeping time. One
second is defined as 9,192,631,770 oscillations of the light.

But a new generation of atomic clocks, known as optical atomic
clocks, outdo the cesium clocks. "Their performance is a lot
better than what currently defines the second," says physicist
Andrew Ludlow of the National Institute of Standards and
Technology in Boulder, Colo. Because those optical atomic clocks
operate at a higher frequency, their "ticks" are more closely
spaced, making them about 100 times more precise than cesium
clocks.

Ideally, the length of a second should be defined using the most
precise timepieces available. A switch might happen in the late
2020s, Ludlow says.

The change to the kilogram's definition was carefully
orchestrated so that it wouldn't affect normal people: A kilogram
of flour still makes the same number of biscuits. Any change to
the second will be similarly coordinated.

So, sorry, there'll be no chance to squeeze any extra seconds
into a day.

https://www.sciencenews.org/article/kilogram-just-got-revamp-unit-time-might-be-next

~ ~ ~

So, perhaps a host of surplus cesium clocks on the market at some point?

73

Dave B G0WBX.

-- 
Created on and sent from a Unix like PC running and using free and open source 
software:


___
time-nuts mailing list -- time-nuts@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@lists.febo.com
To unsubscribe, go to 
http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
and follow the instructions there.