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CC

Chris Caudle

Sat, Dec 9, 2017 5:54 PM

There is a piece missing for me in the articles I have found on new atomic
standards.

This is what I (think I) do understand:
Quantum properties of the atoms can be interrogated using various RF or
optical means to servo the frequency of an oscillator (which could be a
laser based optical oscillator).

The international standard for frequency (based on time) is defined in
terms of a theoretical condition of cesium atoms which cannot be perfectly
achieved in practice, needing absolute zero temperature,
gravity/acceleration equivalent exactly to mean sea level of earth, no
magnetic perturbation, no interaction such as bouncing off of cavity
walls, etc.

New optical standards can achieve "accuracies" of parts in 10^16, verified
by comparing multiple instances of the standards with each other, and if
the standards are built correctly and the theory of operation is correct,
the multiple separate pieces of equipment should agree in frequency output
to within some parts in 10^x, where x has historically been around 15, but
is now reaching toward 17.

So far so good, but here is where I have a gap:
I put "accuracies" in quotations above because as far as I understand you
can actually compare consistency of center frequency or stability over
periods of time between two instances of a particular type of atomic
oscillator, but accuracy in the sense of comparing how closely the the
output frequency matches the calculated theoretical output frequency
(assuming that the operating mechanism is fully understood) is going to
depend on having a reference for comparison that is as good or better than
the new standard to be measured. That implies that the reference has
systematic offset that is known to better than parts in 10^17, but that
would require knowing the quantum properties of the atoms in use to that
level, knowing the gravitational potential at your location to that level,
knowing that the temperature dependence of the equipment was below that
level, etc.

How can anyone ever talk about accuracy in the terms of SI second
definition for these new oscillators? Are they really using layman's
shorthand, and they mean stability and consistency? Or are they really
able to measure all the other factors well enough that they can actually
mean accuracy in the sense of how the SI second definition calls out
absolute zero, gravitational potential, etc.?

--
Chris Caudle

There is a piece missing for me in the articles I have found on new atomic standards. This is what I (think I) do understand: Quantum properties of the atoms can be interrogated using various RF or optical means to servo the frequency of an oscillator (which could be a laser based optical oscillator). The international standard for frequency (based on time) is defined in terms of a theoretical condition of cesium atoms which cannot be perfectly achieved in practice, needing absolute zero temperature, gravity/acceleration equivalent exactly to mean sea level of earth, no magnetic perturbation, no interaction such as bouncing off of cavity walls, etc. New optical standards can achieve "accuracies" of parts in 10^16, verified by comparing multiple instances of the standards with each other, and if the standards are built correctly and the theory of operation is correct, the multiple separate pieces of equipment should agree in frequency output to within some parts in 10^x, where x has historically been around 15, but is now reaching toward 17. So far so good, but here is where I have a gap: I put "accuracies" in quotations above because as far as I understand you can actually compare consistency of center frequency or stability over periods of time between two instances of a particular type of atomic oscillator, but accuracy in the sense of comparing how closely the the output frequency matches the calculated theoretical output frequency (assuming that the operating mechanism is fully understood) is going to depend on having a reference for comparison that is as good or better than the new standard to be measured. That implies that the reference has systematic offset that is known to better than parts in 10^17, but that would require knowing the quantum properties of the atoms in use to that level, knowing the gravitational potential at your location to that level, knowing that the temperature dependence of the equipment was below that level, etc. How can anyone ever talk about accuracy in the terms of SI second definition for these new oscillators? Are they really using layman's shorthand, and they mean stability and consistency? Or are they really able to measure all the other factors well enough that they can actually mean accuracy in the sense of how the SI second definition calls out absolute zero, gravitational potential, etc.? -- Chris Caudle

BA

Bob Albert

Sat, Dec 9, 2017 6:08 PM

So we leave the scientific considerations and delve into the philosophical basis. Somewhere down the line, a standard has to be established, to which all others can be compared. How good this standard is doesn't matter, as long as it's stable. But how does one measure stability? Against what?
The fundamental standard is, I think, the revolution of the earth about the sun. Even that is subject to significant perturbations. If one takes, instead, the resonant frequency of a vibrating atom, as you say it is subject to some variation due to its environment.
So this elusive number will always remain elusive because of its very nature. Yes, one can refine the measurements, but still some uncertainty will remain. And who was the one who said that all cesium atoms are the same? I suspect each atom is unique, that its mass and charge and natural frequency and so on are different for every atom, even though very close.
One could then talk about an average of all cesium atoms but statistically that will only narrow the uncertainty about one order of magnitude.
So the answer to your question is, I believe, that there is no answer to your question. Like slaves we are bound to refine our measurements even though we know we can never reach the absolute.
I ponder a moment and think, well it's probably about 10 o'clock. I look at the clock and find that I am a few minutes off. I think that's close enough for most of my life. I bought a watch that is about a second a day in error so I find myself resetting it often. I am the only one who cares.
Just a few thoughts in passing. Go to the group called Volt Nuts and they go through similar agonies.
Bob
On Saturday, December 9, 2017, 9:55:00 AM PST, Chris Caudle chris@chriscaudle.org wrote:

There is a piece missing for me in the articles I have found on new atomic
standards.

This is what I (think I) do understand:
Quantum properties of the atoms can be interrogated using various RF or
optical means to servo the frequency of an oscillator (which could be a
laser based optical oscillator).

The international standard for frequency (based on time) is defined in
terms of a theoretical condition of cesium atoms which cannot be perfectly
achieved in practice, needing absolute zero temperature,
gravity/acceleration equivalent exactly to mean sea level of earth, no
magnetic perturbation, no interaction such as bouncing off of cavity
walls, etc.

New optical standards can achieve "accuracies" of parts in 10^16, verified
by comparing multiple instances of the standards with each other, and if
the standards are built correctly and the theory of operation is correct,
the multiple separate pieces of equipment should agree in frequency output
to within some parts in 10^x, where x has historically been around 15, but
is now reaching toward 17.

So far so good, but here is where I have a gap:
I put "accuracies" in quotations above because as far as I understand you
can actually compare consistency of center frequency or stability over
periods of time between two instances of a particular type of atomic
oscillator, but accuracy in the sense of comparing how closely the the
output frequency matches the calculated theoretical output frequency
(assuming that the operating mechanism is fully understood) is going to
depend on having a reference for comparison that is as good or better than
the new standard to be measured. That implies that the reference has
systematic offset that is known to better than parts in 10^17, but that
would require knowing the quantum properties of the atoms in use to that
level, knowing the gravitational potential at your location to that level,
knowing that the temperature dependence of the equipment was below that
level, etc.

How can anyone ever talk about accuracy in the terms of SI second
definition for these new oscillators? Are they really using layman's
shorthand, and they mean stability and consistency? Or are they really
able to measure all the other factors well enough that they can actually
mean accuracy in the sense of how the SI second definition calls out
absolute zero, gravitational potential, etc.?

--
Chris Caudle

time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

So we leave the scientific considerations and delve into the philosophical basis. Somewhere down the line, a standard has to be established, to which all others can be compared. How good this standard is doesn't matter, as long as it's stable. But how does one measure stability? Against what? The fundamental standard is, I think, the revolution of the earth about the sun. Even that is subject to significant perturbations. If one takes, instead, the resonant frequency of a vibrating atom, as you say it is subject to some variation due to its environment. So this elusive number will always remain elusive because of its very nature. Yes, one can refine the measurements, but still some uncertainty will remain. And who was the one who said that all cesium atoms are the same? I suspect each atom is unique, that its mass and charge and natural frequency and so on are different for every atom, even though very close. One could then talk about an average of all cesium atoms but statistically that will only narrow the uncertainty about one order of magnitude. So the answer to your question is, I believe, that there is no answer to your question. Like slaves we are bound to refine our measurements even though we know we can never reach the absolute. I ponder a moment and think, well it's probably about 10 o'clock. I look at the clock and find that I am a few minutes off. I think that's close enough for most of my life. I bought a watch that is about a second a day in error so I find myself resetting it often. I am the only one who cares. Just a few thoughts in passing. Go to the group called Volt Nuts and they go through similar agonies. Bob On Saturday, December 9, 2017, 9:55:00 AM PST, Chris Caudle <chris@chriscaudle.org> wrote: There is a piece missing for me in the articles I have found on new atomic standards. This is what I (think I) do understand: Quantum properties of the atoms can be interrogated using various RF or optical means to servo the frequency of an oscillator (which could be a laser based optical oscillator). The international standard for frequency (based on time) is defined in terms of a theoretical condition of cesium atoms which cannot be perfectly achieved in practice, needing absolute zero temperature, gravity/acceleration equivalent exactly to mean sea level of earth, no magnetic perturbation, no interaction such as bouncing off of cavity walls, etc. New optical standards can achieve "accuracies" of parts in 10^16, verified by comparing multiple instances of the standards with each other, and if the standards are built correctly and the theory of operation is correct, the multiple separate pieces of equipment should agree in frequency output to within some parts in 10^x, where x has historically been around 15, but is now reaching toward 17. So far so good, but here is where I have a gap: I put "accuracies" in quotations above because as far as I understand you can actually compare consistency of center frequency or stability over periods of time between two instances of a particular type of atomic oscillator, but accuracy in the sense of comparing how closely the the output frequency matches the calculated theoretical output frequency (assuming that the operating mechanism is fully understood) is going to depend on having a reference for comparison that is as good or better than the new standard to be measured. That implies that the reference has systematic offset that is known to better than parts in 10^17, but that would require knowing the quantum properties of the atoms in use to that level, knowing the gravitational potential at your location to that level, knowing that the temperature dependence of the equipment was below that level, etc. How can anyone ever talk about accuracy in the terms of SI second definition for these new oscillators? Are they really using layman's shorthand, and they mean stability and consistency? Or are they really able to measure all the other factors well enough that they can actually mean accuracy in the sense of how the SI second definition calls out absolute zero, gravitational potential, etc.? -- Chris Caudle _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.

BK

Bob kb8tq

Sat, Dec 9, 2017 6:57 PM

Hi

If you dig back into the various papers on the subject (and the proceedings
that log the post paper questions) the issue of “can we trust the implementation?”
does indeed come up. It’s come up for at least the last 50 years that I’m aware of.
The basic argument runs that for fundamental standards, you need to approach
the process in different ways. You then compare the results from those different
methods. Only after you have done that, do you build confidence in the accuracy
of the various processes. Indeed once you have built confidence in a single approach,
you may decide to all go with that one approach or implementation.

Bob

On Dec 9, 2017, at 12:54 PM, Chris Caudle chris@chriscaudle.org wrote:

There is a piece missing for me in the articles I have found on new atomic
standards.

This is what I (think I) do understand:
Quantum properties of the atoms can be interrogated using various RF or
optical means to servo the frequency of an oscillator (which could be a
laser based optical oscillator).

The international standard for frequency (based on time) is defined in
terms of a theoretical condition of cesium atoms which cannot be perfectly
achieved in practice, needing absolute zero temperature,
gravity/acceleration equivalent exactly to mean sea level of earth, no
magnetic perturbation, no interaction such as bouncing off of cavity
walls, etc.

New optical standards can achieve "accuracies" of parts in 10^16, verified
by comparing multiple instances of the standards with each other, and if
the standards are built correctly and the theory of operation is correct,
the multiple separate pieces of equipment should agree in frequency output
to within some parts in 10^x, where x has historically been around 15, but
is now reaching toward 17.

So far so good, but here is where I have a gap:
I put "accuracies" in quotations above because as far as I understand you
can actually compare consistency of center frequency or stability over
periods of time between two instances of a particular type of atomic
oscillator, but accuracy in the sense of comparing how closely the the
output frequency matches the calculated theoretical output frequency
(assuming that the operating mechanism is fully understood) is going to
depend on having a reference for comparison that is as good or better than
the new standard to be measured. That implies that the reference has
systematic offset that is known to better than parts in 10^17, but that
would require knowing the quantum properties of the atoms in use to that
level, knowing the gravitational potential at your location to that level,
knowing that the temperature dependence of the equipment was below that
level, etc.

How can anyone ever talk about accuracy in the terms of SI second
definition for these new oscillators? Are they really using layman's
shorthand, and they mean stability and consistency? Or are they really
able to measure all the other factors well enough that they can actually
mean accuracy in the sense of how the SI second definition calls out
absolute zero, gravitational potential, etc.?

--
Chris Caudle

time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Hi If you dig back into the various papers on the subject (and the proceedings that log the post paper questions) the issue of “can we trust the implementation?” does indeed come up. It’s come up for at least the last 50 years that I’m aware of. The basic argument runs that for fundamental standards, you need to approach the process in different ways. You then compare the results from those different methods. Only after you have done that, do you build confidence in the accuracy of the various processes. Indeed once you have built confidence in a single approach, you may decide to all go with that one approach or implementation. Bob > On Dec 9, 2017, at 12:54 PM, Chris Caudle <chris@chriscaudle.org> wrote: > > There is a piece missing for me in the articles I have found on new atomic > standards. > > This is what I (think I) do understand: > Quantum properties of the atoms can be interrogated using various RF or > optical means to servo the frequency of an oscillator (which could be a > laser based optical oscillator). > > The international standard for frequency (based on time) is defined in > terms of a theoretical condition of cesium atoms which cannot be perfectly > achieved in practice, needing absolute zero temperature, > gravity/acceleration equivalent exactly to mean sea level of earth, no > magnetic perturbation, no interaction such as bouncing off of cavity > walls, etc. > > New optical standards can achieve "accuracies" of parts in 10^16, verified > by comparing multiple instances of the standards with each other, and if > the standards are built correctly and the theory of operation is correct, > the multiple separate pieces of equipment should agree in frequency output > to within some parts in 10^x, where x has historically been around 15, but > is now reaching toward 17. > > So far so good, but here is where I have a gap: > I put "accuracies" in quotations above because as far as I understand you > can actually compare consistency of center frequency or stability over > periods of time between two instances of a particular type of atomic > oscillator, but accuracy in the sense of comparing how closely the the > output frequency matches the calculated theoretical output frequency > (assuming that the operating mechanism is fully understood) is going to > depend on having a reference for comparison that is as good or better than > the new standard to be measured. That implies that the reference has > systematic offset that is known to better than parts in 10^17, but that > would require knowing the quantum properties of the atoms in use to that > level, knowing the gravitational potential at your location to that level, > knowing that the temperature dependence of the equipment was below that > level, etc. > > How can anyone ever talk about accuracy in the terms of SI second > definition for these new oscillators? Are they really using layman's > shorthand, and they mean stability and consistency? Or are they really > able to measure all the other factors well enough that they can actually > mean accuracy in the sense of how the SI second definition calls out > absolute zero, gravitational potential, etc.? > > -- > Chris Caudle > > > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there.

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Re: [time-nuts] IEEE Spectrum - Dec 2017 - article on chip-scale atomic frequency reference