[HN Gopher] New atomic fountain clock joins group that keeps the...
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New atomic fountain clock joins group that keeps the world on time
Author : austinallegro
Score : 87 points
Date : 2025-04-29 12:39 UTC (1 days ago)
(HTM) web link (www.nist.gov)
(TXT) w3m dump (www.nist.gov)
| throw0101a wrote:
| 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 wrote:
| 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!)
| move-on-by wrote:
| 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 wrote:
| The Naval Observatory in Washington DC has quite a few also
| CamperBob2 wrote:
| 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-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 ), but that probably won't shake up
| the existing market too much.
| fanf2 wrote:
| As well as NIST there is Schriever spave 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 wrote:
| 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 wrote:
| Curiously, there's also a contender for the worst, which I
| think at present is the gravitational constant.
| teraflop wrote:
| 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 wrote:
| > 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)
| post-2019, if my understanding of it is correct?
| AlotOfReading wrote:
| That's around the same sensitivity that LIGO operates at.
| CGMthrowaway wrote:
| 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-...
| RetroTechie wrote:
| 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 wrote:
| 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...
|
| https://spectrum.ieee.org/chipscale-atomic-clock
|
| Microchip launched their latest version earlier this year:
|
| https://www.electronicspecifier.com/products/frequency-contr...
| Palomides wrote:
| I've heard they're struggling to get good consistent
| perfomance on them compared to other alternatives in similar
| sizes
| WarOnPrivacy wrote:
| > 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 wrote:
| 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/co...
|
| [2] https://www.teledyne-si.com/en-us/Products-and-
| Services_/Pag...
| ginko wrote:
| Any idea what one of those would cost? (and where to buy
| them?)
| nullc wrote:
| SA.45s (and the eval board) has been on mouser in the past,
| I'm not sure if they carry it now because mouser
| continually blocks me these days. It was previously around
| $1500.
|
| If you're interested in a small atomic clock and don't
| absolutely require the very low power consumption of the
| SA.45s and the very small package size you can get better
| performance, reliability, and cost in something a big
| larger and quite a bit higher power consumption.
|
| The CSAC improved atomic oscillators a lot more in power
| than size... but its timekeeping performance is so/so as
| far as atomic clocks go.
|
| In particular, the surplus market has a lot of telecom
| rubidium that can be had quite inexpensively.
|
| I'm personally a fan of the PRS-10 (which also exists in a
| benchtop form, the SRS725). They seem to regularly sell on
| ebay for about $300 with a little breakout board for power.
| And unlike many small rubidiums they have very good phase
| noise. You can sync them to GPS time using a 1pps input
| (though I believe on the bare modules the 1pps sync is
| optional so if you want to use it be sure to get one that
| has it).
| RetroTechie wrote:
| _> The CSAC improved atomic oscillators a lot more in
| power than size... but its timekeeping performance is
| so/so as far as atomic clocks go._
|
| Timekeeping of atomic clocks is still waaaayy better than
| next-best technologies (like temp-compensated Xtal
| oscillators). And size/power/$ constraints matter. So
| CSACs for the win imho.
| fsh wrote:
| A $5 GPS receiver runs circles around a CSAC, so the
| range of useful applications is quite limited.
| nullc wrote:
| The timing output from a $5 gps receiver isn't
| particularly impressive. You have to go to pretty long
| time intervals for a non-timing GPS to win out. Depending
| on your application those intervals may be thoroughly
| irrelevant, e.g. using the device as a frequency source
| rather than a clock.
|
| There is also, of course, the issue of infrastructure
| dependence. Particularly since wireless telephony has
| moved almost exclusively to GNSS time we're going to have
| a really bad time if kessler syndrome takes out the GNSS
| satellites.
|
| Edit: Here is an example adev chart for a inexpensive
| atomic clock vs what appears to be a pretty good timing
| GPS receiver: https://www.thinksrs.com/images/instr/prs10
| /PRS10diag2LG.gif
|
| So in that case the GPS accuracy only beats out the free
| running atomic clock at intervals greater than 200,000
| seconds or so.
|
| Here is a collection of older timing receivers:
| http://www.leapsecond.com/pages/3gps/gps-adev-mdev.gif
|
| A quick look didn't turn up any cheap non-timing
| receivers, but my experience is they're pretty bad (I
| mean relative to atomic standards, of course).
|
| There are better timing receivers than the ones charted
| above, of course, but they are not $5. Their cost is now
| in the same general ballpark as surplus atomic clocks.
|
| Of course, if you have both you can sync one to the other
| with whatever time constant maximizes the composite
| performance and have the best of both.
|
| (and primary atomic clocks don't have this drift issue,
| but sadly the days of the occasional sub $1000 5071
| showing up on auction sites seem to be over. :P )
| schoen wrote:
| > SA.45s (and the eval board) has been on mouser in the
| past, I'm not sure if they carry it now because mouser
| continually blocks me these days. It was previously
| around $1500.
|
| I searched on Mouser and found that part no longer has a
| listed price; there are fancier chip-scale atomic clocks
| from the same company, the only one with a listed price
| going for $3,528.23.
|
| Others from a different manufacturer are just over
| $2,000. A kind of awesome thing is that one of those
| chips is marked
|
| Frequency 10.000000 MHz
|
| It's awesome that that's not just an estimate or some
| kind of exaggeration!
| alnwlsn wrote:
| How big is big? You can still get used FE-5680A rubidiums on
| Ebay for a few hundred. They are about the size of a small book
| and need ~20 watts.
|
| Not sure how good/useful/not broken they are since I've never
| had one, but over the last 10 years I've seen them in a good
| number of hobbyist projects.
|
| Or you could just go for GPS. That's technically still atomic
| clocks, but in space!
| WarOnPrivacy wrote:
| NIST explainer: Cesium Fountain Clock [1999]
|
| https://www.nist.gov/news-events/news/1999/12/nist-f1-cesium...
| infogulch wrote:
| 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 | Major Leap for
| Nuclear Clock Paves Way for Ultraprecise Timekeeping (nist.gov)
| 0cf8612b2e1e wrote:
| 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 wrote:
| Like this https://www.youtube.com/watch?v=RzOQHazjXvE
| nullc wrote:
| 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 wrote:
| 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
| nullc wrote:
| Having to use vacuum UV is a bit of a bummer... just doing
| anything inside a vacuum is a PITA.
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