5 ms·

New atomic fountain clock joins group that keeps the world on time

118 points by austinallegro 1y ago

throw0101a 1y ago
What are 'limits' on how accurate enough clocks 'should' be? Presumably there's diminishing returns, but as the article says we're at one part in 2.2e-16, are there practical application of going further?
- 0_____0 1y ago
  With radio astronomy, where you're measuring phase of incoming radiation, I think "more is more" applies. Would be interesting to hear from someone who actually has experience in that domain though (not me!)
- maxnoe 1y ago
  The current goal is to redefine the second in terms of an optical frequency once clocks are available that offer a higher precision than 1 second over the lifetime of the universe. https://www.nist.gov/si-redefinition/second-future https://www.nist.gov/si-redefinition/second-future
- slowmovintarget 1y ago
  This may not count as practical, but with high-enough resolution on time we can start to make direct observations of relativistic effects. There are physicists like Ivette Fuentes starting to do direct experiments with time dilation [1]. When Einstein made his thought experiments with light clocks and described what should be observed, he didn't think we'd actually make light clocks... but we have the technology to do that literally (really, truly, actually... so sad we no longer have a word in English that means that). [1] https://www.youtube.com/watch?v=y5V9qAETcw8 https://www.youtube.com/watch?v=y5V9qAETcw8
move-on-by 1y ago
How many atomic clocks are in operation in Colorado now? It would be nice if they could be spread around a bit. I suppose there are logistical issues that keep them centralized?
- algorithmsRcool 1y ago
  The Naval Observatory in Washington DC has quite a few also
- CamperBob2 1y ago
  Commercial atomic clocks of various types aren't that rare. Every cell site has a rubidium standard and/or GPS timing, many data centers probably have a cesium standard, and radio astronomers use H-masers for interferometry. Everybody with a GPS-disciplined oscillator has access to time and frequency from the Naval Observatory at the sub-100 ns level, optionally augmented to +/- 1 ns with reasonably affordable gear like https://www.sparkfun.com/sparkpnt-gnss-disciplined-oscillator.html https://www.sparkfun.com/sparkpnt-gnss-disciplined-oscillato... . A fountain clock is on a whole different level than any of these. The same researchers who build fountains also work on even better optical lattice clocks, none of which you can buy from Sparkfun. These are research tools that don't have a market, at least not yet. The SI second definition will likely move from Cs-133 at 9 GHz to Sr-87 at 400 THz before too long ( https://www.nist.gov/si-redefinition/second-future https://www.nist.gov/si-redefinition/second-future ), but that probably won't shake up the existing market too much.
- fanf2 1y ago
  As well as NIST there is Schriever spave force base https://en.m.wikipedia.org/wiki/Schriever_Space_Force_Base https://en.m.wikipedia.org/wiki/Schriever_Space_Force_Base which is the ground operations centre for GPS. They have the USNO alternate master clock, which maintains a copy of the USNO time scale based on caesium beam and rubidium fountain clocks.
algorithmsRcool 1y ago
I recall reading that our ability to measure time accurately exceeds that of any other quantity. According to the NIST, the newest Optical Lattice clocks would drift by less than 1 second if they were started 13 billion years ago at the big bang. What else can we measure down past 1 part per 10e18?
- analog31 1y ago
  Curiously, there's also a contender for the worst, which I think at present is the gravitational constant.
  - teraflop 1y ago
    Yup. And an interesting detail is that we know the product G·M_e (where G is the gravitational constant, and M_e is the mass of the earth) to much higher precision than we know either of its factors. And the same goes for the sun and most of the other planets. This is because the motion of celestial bodies and spacecraft is dominated by gravitational forces which depend only on G·M, and that motion can be measured extremely accurately with e.g. Doppler radar.
- ipdashc 1y ago
  > our ability to measure time accurately exceeds that of any other quantity TIL. I guess maybe that explains why the second is used as the base of the SI (https://en.wikipedia.org/wiki/2019_revision_of_the_SI https://en.wikipedia.org/wiki/2019_revision_of_the_SI) post-2019, if my understanding of it is correct?
- AlotOfReading 1y ago
  That's around the same sensitivity that LIGO operates at.
CGMthrowaway 1y ago
Can't mention a fountain clock without calling to mind one the Lion Clock in Alhambra Palace, of my favorite things ever: https://www.iflscience.com/this-incredible-islamic-fountain-from-the-1300s-might-have-actually-been-a-clock-77044 https://www.iflscience.com/this-incredible-islamic-fountain-...
RetroTechie 1y ago
Some years back there was talk of an atomic clock that came in a very small package (matchbox / cigarette pack size?). Iirc, saw a price indication of $1500 somewhere. Something like that still around, and/or available? Any updated designs? Personally I have no need for ultra-accurate timekeeping. But hey... an atomic clock is way cooler than a Nixie clock or oven-controlled Xtal oscillator. And no... huge 2nd hand atomic clock found on eBay etc doesn't cut it. Too big /heavy / power-hungry.
- philipkglass 1y ago
  You're thinking of the Chip Scale Atomic Clock, first demonstrated by NIST in 2003 and commercialized in 2011: https://www.nist.gov/noac/technology/time-and-frequency/chip-scale-clocks https://www.nist.gov/noac/technology/time-and-frequency/chip... https://spectrum.ieee.org/chipscale-atomic-clock https://spectrum.ieee.org/chipscale-atomic-clock Microchip launched their latest version earlier this year: https://www.electronicspecifier.com/products/frequency-control/microchip-releases-next-gen-atomic-clock https://www.electronicspecifier.com/products/frequency-contr...
  - Palomides 1y ago
    I've heard they're struggling to get good consistent perfomance on them compared to other alternatives in similar sizes
  - WarOnPrivacy 1y ago
    > Microchip launched their latest version earlier this year: Spectratime's version (mRO-50) went into a $2M piece of eye-candy that mechanically syncs a watch. https://www.urwerk.com/collections/ur-chronometry/amc https://www.urwerk.com/sites/default/files/press/docs/urwerk_amc_eng.pdf
- ooterness 1y ago
  You're probably thinking of chip-scale atomic clocks (CSAC). There's at least two companies that make them [1][2]. [1] https://www.microchip.com/en-us/products/clock-and-timing/components/atomic-clocks/embedded-atomic-oscillators/csac https://www.microchip.com/en-us/products/clock-and-timing/co... [2] https://www.teledyne-si.com/en-us/Products-and-Services_/Pages/Teledyne-Chip-Scale-Atomic-Clock.aspx https://www.teledyne-si.com/en-us/Products-and-Services_/Pag...
WarOnPrivacy 1y ago
NIST explainer: Cesium Fountain Clock [1999] https://www.nist.gov/news-events/news/1999/12/nist-f1-cesium-fountain-clock https://www.nist.gov/news-events/news/1999/12/nist-f1-cesium...
infogulch 1y ago
Cesium-based atomic clocks ("fountain clocks") like these use the natural resonance frequency of electron orbital energy states under a microwave laser which can be counted to measure time. Since there is a natural background noise of microwaves and many frequencies can interact with orbitals it's important to isolate the atoms from outside sources of electromagnetic radiation and heat in order to maintain accuracy. Earlier this year there was a big leap in so-called "nuclear clocks" which uses the resonant frequency of energy states of a nucleus itself as opposed to electron orbitals around it. Besides the "more frequency = more better" factor that has always driven clock accuracy -- thorium-229 nuclei excites in ultraviolet wavelengths -- nuclear clocks are better isolated than electron orbital-based clocks because the frequency band where they interact is impossibly narrow. In fact, the reason why it was only recently demonstrated is due to the difficulty of producing the required frequency at a high enough precision to interact reliably. This could lead to more accurate and more compact and cheaper clocks. Discussion 4 months ago: https://news.ycombinator.com/item?id=42362215 https://news.ycombinator.com/item?id=42362215 | Major Leap for Nuclear Clock Paves Way for Ultraprecise Timekeeping (nist.gov)
0cf8612b2e1e 1y ago
How do you sync atomic clocks? When the error rate is 1/1e16, your error in propagating the time from one clock to another is going to be off by many orders of magnitude vs the timekeeper itself.
- alnwlsn 1y ago
  Like this https://www.youtube.com/watch?v=RzOQHazjXvE https://www.youtube.com/watch?v=RzOQHazjXvE
- nullc 1y ago
  The modern approach is common view time transfer. Both clocks can observe signal sources such as satellites and compute their relative offsets. The signal doesn't need to be particularly accurate (though it doesn't hurt), though you do need a good model of its position and propagation. GNSS satellites are an obvious choice though there are also specialized services for CVTT. Note that this is distinct from syncing from GPS, which is a thing people obviously do too, but CVTT can achieve much higher accuracy. Because you're synchronizing extremely stable clocks the difference between them will primary be an offset (plus/minus a slope from relativistic effects of different altitude). Because of this you can average a large number of readings, so the only major source of error will be systematic effects in propagation/orbit/etc. Historically, sync was obtained via traveling clocks-- e.g. you sync one atomic clock up and load it, running, in a station wagon... which is the same thing that is most often done for voltage standards today (as atomic voltage standards remain rare, compared to atomic clocks-- I think the least I've paid for one is $15 excluding the ones that were free). But vibration isn't great for anything with a crystal oscillator in it, and the most modern atomic fountain clocks don't work if they're accelerating in any direction except the designed 'up' direction (gravity), because the little cloud of cooled atoms will fall out of the measurement channel, which makes sync by station wagon not viable. Of course, once you talk about syncing there is always a question of what you're syncing to. UTC doesn't exist until after the fact. Laboratories measure their offsets via CVTT and UTC is calculated after the fact as past offsets to each of the contributing clocks.
geerlingguy 1y ago
New goal: upgrading from a Rubidium CSAC to NIST-F4. I've also been reading about nuclear clocks[1]... skipping over the uncertainty of the entire atom's chaotic oscillations entirely! [1] https://en.wikipedia.org/wiki/Nuclear_clock https://en.wikipedia.org/wiki/Nuclear_clock
- nullc 1y ago
  Having to use vacuum UV is a bit of a bummer... just doing anything inside a vacuum is a PITA.

118 points by austinallegro 1y ago

What are 'limits' on how accurate enough clocks 'should' be? Presumably there's diminishing returns, but as the article says we're at one part in 2.2e-16, are there practical application of going further?

0_____0 1y ago
With radio astronomy, where you're measuring phase of incoming radiation, I think "more is more" applies. Would be interesting to hear from someone who actually has experience in that domain though (not me!)
maxnoe 1y ago
The current goal is to redefine the second in terms of an optical frequency once clocks are available that offer a higher precision than 1 second over the lifetime of the universe. https://www.nist.gov/si-redefinition/second-future https://www.nist.gov/si-redefinition/second-future
slowmovintarget 1y ago
This may not count as practical, but with high-enough resolution on time we can start to make direct observations of relativistic effects. There are physicists like Ivette Fuentes starting to do direct experiments with time dilation [1]. When Einstein made his thought experiments with light clocks and described what should be observed, he didn't think we'd actually make light clocks... but we have the technology to do that literally (really, truly, actually... so sad we no longer have a word in English that means that). [1] https://www.youtube.com/watch?v=y5V9qAETcw8 https://www.youtube.com/watch?v=y5V9qAETcw8

move-on-by 1y ago

How many atomic clocks are in operation in Colorado now? It would be nice if they could be spread around a bit. I suppose there are logistical issues that keep them centralized?

algorithmsRcool 1y ago
The Naval Observatory in Washington DC has quite a few also
CamperBob2 1y ago
Commercial atomic clocks of various types aren't that rare. Every cell site has a rubidium standard and/or GPS timing, many data centers probably have a cesium standard, and radio astronomers use H-masers for interferometry. Everybody with a GPS-disciplined oscillator has access to time and frequency from the Naval Observatory at the sub-100 ns level, optionally augmented to +/- 1 ns with reasonably affordable gear like https://www.sparkfun.com/sparkpnt-gnss-disciplined-oscillator.html https://www.sparkfun.com/sparkpnt-gnss-disciplined-oscillato... . A fountain clock is on a whole different level than any of these. The same researchers who build fountains also work on even better optical lattice clocks, none of which you can buy from Sparkfun. These are research tools that don't have a market, at least not yet. The SI second definition will likely move from Cs-133 at 9 GHz to Sr-87 at 400 THz before too long ( https://www.nist.gov/si-redefinition/second-future https://www.nist.gov/si-redefinition/second-future ), but that probably won't shake up the existing market too much.
fanf2 1y ago
As well as NIST there is Schriever spave force base https://en.m.wikipedia.org/wiki/Schriever_Space_Force_Base https://en.m.wikipedia.org/wiki/Schriever_Space_Force_Base which is the ground operations centre for GPS. They have the USNO alternate master clock, which maintains a copy of the USNO time scale based on caesium beam and rubidium fountain clocks.

algorithmsRcool 1y ago

I recall reading that our ability to measure time accurately exceeds that of any other quantity. According to the NIST, the newest Optical Lattice clocks would drift by less than 1 second if they were started 13 billion years ago at the big bang. What else can we measure down past 1 part per 10e18?

analog31 1y ago
Curiously, there's also a contender for the worst, which I think at present is the gravitational constant.
- teraflop 1y ago
  Yup. And an interesting detail is that we know the product G·M_e (where G is the gravitational constant, and M_e is the mass of the earth) to much higher precision than we know either of its factors. And the same goes for the sun and most of the other planets. This is because the motion of celestial bodies and spacecraft is dominated by gravitational forces which depend only on G·M, and that motion can be measured extremely accurately with e.g. Doppler radar.
ipdashc 1y ago
> our ability to measure time accurately exceeds that of any other quantity TIL. I guess maybe that explains why the second is used as the base of the SI (https://en.wikipedia.org/wiki/2019_revision_of_the_SI https://en.wikipedia.org/wiki/2019_revision_of_the_SI) post-2019, if my understanding of it is correct?
AlotOfReading 1y ago
That's around the same sensitivity that LIGO operates at.

CGMthrowaway 1y ago

Can't mention a fountain clock without calling to mind one the Lion Clock in Alhambra Palace, of my favorite things ever: https://www.iflscience.com/this-incredible-islamic-fountain-from-the-1300s-might-have-actually-been-a-clock-77044 https://www.iflscience.com/this-incredible-islamic-fountain-...

RetroTechie 1y ago

Some years back there was talk of an atomic clock that came in a very small package (matchbox / cigarette pack size?). Iirc, saw a price indication of $1500 somewhere. Something like that still around, and/or available? Any updated designs? Personally I have no need for ultra-accurate timekeeping. But hey... an atomic clock is way cooler than a Nixie clock or oven-controlled Xtal oscillator. And no... huge 2nd hand atomic clock found on eBay etc doesn't cut it. Too big /heavy / power-hungry.

philipkglass 1y ago
You're thinking of the Chip Scale Atomic Clock, first demonstrated by NIST in 2003 and commercialized in 2011: https://www.nist.gov/noac/technology/time-and-frequency/chip-scale-clocks https://www.nist.gov/noac/technology/time-and-frequency/chip... https://spectrum.ieee.org/chipscale-atomic-clock https://spectrum.ieee.org/chipscale-atomic-clock Microchip launched their latest version earlier this year: https://www.electronicspecifier.com/products/frequency-control/microchip-releases-next-gen-atomic-clock https://www.electronicspecifier.com/products/frequency-contr...
- Palomides 1y ago
  I've heard they're struggling to get good consistent perfomance on them compared to other alternatives in similar sizes
- WarOnPrivacy 1y ago
  > Microchip launched their latest version earlier this year: Spectratime's version (mRO-50) went into a $2M piece of eye-candy that mechanically syncs a watch. https://www.urwerk.com/collections/ur-chronometry/amc https://www.urwerk.com/sites/default/files/press/docs/urwerk_amc_eng.pdf
ooterness 1y ago
You're probably thinking of chip-scale atomic clocks (CSAC). There's at least two companies that make them [1][2]. [1] https://www.microchip.com/en-us/products/clock-and-timing/components/atomic-clocks/embedded-atomic-oscillators/csac https://www.microchip.com/en-us/products/clock-and-timing/co... [2] https://www.teledyne-si.com/en-us/Products-and-Services_/Pages/Teledyne-Chip-Scale-Atomic-Clock.aspx https://www.teledyne-si.com/en-us/Products-and-Services_/Pag...

WarOnPrivacy 1y ago

NIST explainer: Cesium Fountain Clock [1999] https://www.nist.gov/news-events/news/1999/12/nist-f1-cesium-fountain-clock https://www.nist.gov/news-events/news/1999/12/nist-f1-cesium...

infogulch 1y ago

Cesium-based atomic clocks ("fountain clocks") like these use the natural resonance frequency of electron orbital energy states under a microwave laser which can be counted to measure time. Since there is a natural background noise of microwaves and many frequencies can interact with orbitals it's important to isolate the atoms from outside sources of electromagnetic radiation and heat in order to maintain accuracy. Earlier this year there was a big leap in so-called "nuclear clocks" which uses the resonant frequency of energy states of a nucleus itself as opposed to electron orbitals around it. Besides the "more frequency = more better" factor that has always driven clock accuracy -- thorium-229 nuclei excites in ultraviolet wavelengths -- nuclear clocks are better isolated than electron orbital-based clocks because the frequency band where they interact is impossibly narrow. In fact, the reason why it was only recently demonstrated is due to the difficulty of producing the required frequency at a high enough precision to interact reliably. This could lead to more accurate and more compact and cheaper clocks. Discussion 4 months ago: https://news.ycombinator.com/item?id=42362215 https://news.ycombinator.com/item?id=42362215 | Major Leap for Nuclear Clock Paves Way for Ultraprecise Timekeeping (nist.gov)

0cf8612b2e1e 1y ago

How do you sync atomic clocks? When the error rate is 1/1e16, your error in propagating the time from one clock to another is going to be off by many orders of magnitude vs the timekeeper itself.

alnwlsn 1y ago
Like this https://www.youtube.com/watch?v=RzOQHazjXvE https://www.youtube.com/watch?v=RzOQHazjXvE
nullc 1y ago
The modern approach is common view time transfer. Both clocks can observe signal sources such as satellites and compute their relative offsets. The signal doesn't need to be particularly accurate (though it doesn't hurt), though you do need a good model of its position and propagation. GNSS satellites are an obvious choice though there are also specialized services for CVTT. Note that this is distinct from syncing from GPS, which is a thing people obviously do too, but CVTT can achieve much higher accuracy. Because you're synchronizing extremely stable clocks the difference between them will primary be an offset (plus/minus a slope from relativistic effects of different altitude). Because of this you can average a large number of readings, so the only major source of error will be systematic effects in propagation/orbit/etc. Historically, sync was obtained via traveling clocks-- e.g. you sync one atomic clock up and load it, running, in a station wagon... which is the same thing that is most often done for voltage standards today (as atomic voltage standards remain rare, compared to atomic clocks-- I think the least I've paid for one is $15 excluding the ones that were free). But vibration isn't great for anything with a crystal oscillator in it, and the most modern atomic fountain clocks don't work if they're accelerating in any direction except the designed 'up' direction (gravity), because the little cloud of cooled atoms will fall out of the measurement channel, which makes sync by station wagon not viable. Of course, once you talk about syncing there is always a question of what you're syncing to. UTC doesn't exist until after the fact. Laboratories measure their offsets via CVTT and UTC is calculated after the fact as past offsets to each of the contributing clocks.

geerlingguy 1y ago

New goal: upgrading from a Rubidium CSAC to NIST-F4. I've also been reading about nuclear clocks[1]... skipping over the uncertainty of the entire atom's chaotic oscillations entirely! [1] https://en.wikipedia.org/wiki/Nuclear_clock https://en.wikipedia.org/wiki/Nuclear_clock

nullc 1y ago
Having to use vacuum UV is a bit of a bummer... just doing anything inside a vacuum is a PITA.