Re: [time-nuts] Cold Rubidium over hyped?
Moin, On Fri, 8 Nov 2019 14:33:45 -0800 wrote: > Well I have been looking at the data in the > > https://www.researchgate.net/publication/325499937_A_portable_cold_87_Rb_ > atomic_clock_with_frequency_instability_at_one_day_in_the_10-15_range > > link and find that maybe they are overstating their performance! > > In the plot of figure 5 my HP 5065A almost perfectly matches the Allan > deviation > out to 1000 Sec.! (Although mine does have VERY good performance) And you don't think this is impressive? Short term performance of an atomic clock depends on the SNR of the signal. Which in turn depends on the number of atoms being probed. A vapor cell standard probes billions of atoms even for tiny cells, 1e15 to 1e18 for large cells. A MOT usually traps a few 10k to at most a few tens of million of atoms. Ie we are at least a factor of 1000 below a Rb vapor cell, and more like a factor of billions. And as usual, noise goes down with the square root. Which in turn means the theoretical SNR in a cold atom Rb standard is a factor of 10'000 lower than your 5065! Yet it achieves the same short term performance! (The real differnence in SNR is probably lower than that, but I doubt it's less than a factor of 100) And mind you, we are still talking about quite new products where little optimization has been done. And we aren't talking about big companies like HP either. µQuans was started by a few students, who made their research into a product. SDI is a very small business. Neither have millions to spend on optimizing the product until it's perfect before they announce it to the world. They had to get a product out as soon as possible to make sure they can recapture the cost of development. And don't worry, both are working on improving the system. To make things worse, the paper you are citing is actually the first one SDI published. Meaning that was (one of?) the first complete system they had built. > Also if you look at figure 7 all the Maser data shown seems to be from > poorly > operating Masers so any judgement of better clock performance versus the > Masers > is a bit much! Calling the masers of NIST poorly maintained is a bit much, isn't it? Besides, they do not measure against the masers, but against UTC(NIST), though that's not that clear from the paper, as they only say "NIST measurement system." Other papers state it explicitly. > Something does not add up in their data! I think it clear from what I wrote above and what others wrote before me that you are comparing apples and oranges. While it is true that both the cold atom clocks and your 5065 use Rubidium as a species, the techniques involved are so differnt that you have to treat them as a totally different kind of clock. If you look at them as a active H maser or Cs beam standard replacement, that would be closer to what they are. On Sat, 09 Nov 2019 00:07:43 + "Poul-Henning Kamp" wrote: > Given that these two cold-Rb devices are 1st generation of their > kind and given how little time they have had to collect data on > them yet, both with respect to performance but also day-to-day > gremlin-wrangling, I wouldnt be at all surprised if the next > two generations of that concept delivers almost two orders of > magnitude improved performance. While both companies are working on improvements. I don't expect two orders of magnitude. Both systems work close to what the theoretical limit of the number of atoms they are probing are. I wouldn't be surprised if they get a factor of 10 out of the system, after all improvements have been done. But I would find it unlikely that the reach a factor of 100 without significantly increasing the number of atoms they probe or increasing the interogation time. And both of these things are quite hard to do in these architectures. On Sat, 09 Nov 2019 07:05:10 + "Poul-Henning Kamp" wrote: > It is not like people have not been improving the Rb-Gas-cell, but if > you want to improve it an order of magnitude all the myriad of "small > issues" to fix add up real fast, and when you are done with all of > it, you will still have frequency drift. If you want to know what the limit of Rb vapor cell standards are, have a look at the research done by the group of Mileti and Affolderbach. They are at ~1e-13/sqrt(tau) and are trying to push it down to the shot noise limit (which is at a few parts in 1e-14). That's the limit you can do. And that's still not accounting for drift and other things which limit the ADEV to a few parts in 1e-14 somewhere around a tau of 1k to 10k. On Sat, 9 Nov 2019 02:38:45 +0100 Magnus Danielson wrote: > This is well understood techniques now, so that it matures into > commercial products is not strange. It's worth noting that optically > probed cesium also exists from Oscilloquartz, altering the beam standard > techniques It is also worth noting that it took Oscilloquartz several years to get it working. And not only that, a lot of people in industry
Re: [time-nuts] Cold Rubidium over hyped?
Hi > On Nov 8, 2019, at 11:18 PM, cdel...@juno.com wrote: > > The pressure sensitivity for a classic design can easily be eliminated. > > I'm pretty sure that the old Varian R20 cell was mostly immune. > > Either using the R20 design or stiffer convex ends in a modern design > would work. > > Also a sealed optical unit has been used to get rid of the pressure > problem. OCXO’s have a pressure sensitivity as well. There, the only real answer is a welded enclosure. Anything short of that simply integrates the pressure via low leak rates and makes things even stranger ….. Bob > > Any of these methods would be trivial in a new design. > > The Rb/glass absorption is mostly in the lamp, when using the proper > glasses in the cell and using similar lasers to what the cold standard > uses eliminates that. > > Newer RF architecture would also help, NLDL multiplier, low noise > synthesis, etc. > > My main gripe was that either they were either intentionally reducing the > performance of their masers or using a setup that did not do justice to > them. > > Cheers, > > Corby > > > ___ > 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] Cold Rubidium over hyped?
Hi, On 2019-11-09 08:05, Poul-Henning Kamp wrote: > > In message , cdel...@juno.com writes: > > [long list of all the work to be done before the classical gas-cell Rb > improves materially] > > You are sort of making my point here Corby. > > It is not like people have not been improving the Rb-Gas-cell, but if > you want to improve it an order of magnitude all the myriad of "small > issues" to fix add up real fast, and when you are done with all of > it, you will still have frequency drift. > ... and these devices address a different aspect as per Michael's point. It's not for the phase-noise, but for long-term stability, so that would be instead of cesium beams or fountains. Gas-cell standards cannot really solve that because the myriad of issues turn out an unknown device frequency shift, which altought can be stable is not suitable as standard. Rather, these devices could allow for much more affordable contribution to the second/TAI rate in international timekeeping. Cheers, Magnus ___ 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] Cold Rubidium over hyped?
In message , cdel...@juno.com writes: [long list of all the work to be done before the classical gas-cell Rb improves materially] You are sort of making my point here Corby. It is not like people have not been improving the Rb-Gas-cell, but if you want to improve it an order of magnitude all the myriad of "small issues" to fix add up real fast, and when you are done with all of it, you will still have frequency drift. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ 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] Cold Rubidium over hyped?
The pressure sensitivity for a classic design can easily be eliminated. I'm pretty sure that the old Varian R20 cell was mostly immune. Either using the R20 design or stiffer convex ends in a modern design would work. Also a sealed optical unit has been used to get rid of the pressure problem. Any of these methods would be trivial in a new design. The Rb/glass absorption is mostly in the lamp, when using the proper glasses in the cell and using similar lasers to what the cold standard uses eliminates that. Newer RF architecture would also help, NLDL multiplier, low noise synthesis, etc. My main gripe was that either they were either intentionally reducing the performance of their masers or using a setup that did not do justice to them. Cheers, Corby ___ 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] Cold Rubidium over hyped?
On 11/8/19 5:38 PM, Magnus Danielson wrote: So, while hydrogen masers may work and large cell rubidiums can be cleaned up, eventually we come to the point where these new techniques will take over for many good reasons. Maybe one day we will have time-nuts with cold rubidium clocks and maybe even optical clocks. Or Mercury or Strontium ion? ___ 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] Cold Rubidium over hyped?
Hi, On 2019-11-09 01:07, Poul-Henning Kamp wrote: > > In message , cdel...@juno.com writes: > >> Just wonder if some 5065A can get so impressive that they don't just >> make a modern large/cool cell classic Rubidium with modern electronics >> technology! Certainly would be cheaper and more long lived also. > But isn't that essentially what they have done ? Yes. > > The Rb-lamp-filter thing has been beaten to death. Its not like > people have not researched it in the last 50 years, but nobody > anywhere have found a way to get rid of the Rb/glass absorption > related aging or the pressure-sensitivity for that matter, so 5065 > performance pretty much is the best you can ever hope for there > as long as your customers are terrestial. The wall shift, the buffer gas shift, the resonator shift and how these relate to environmentals in addition to the lamp intensity shift. All well researched. Rubidium as such is not a bad species to measure, on the contrary, we learned that it excels over cesium in laser cooled state, as the cross-section is smaller. > > Given that these two cold-Rb devices are 1st generation of their > kind and given how little time they have had to collect data on > them yet, both with respect to performance but also day-to-day > gremlin-wrangling, I wouldnt be at all surprised if the next > two generations of that concept delivers almost two orders of > magnitude improved performance. Long-term measurements is being done at NIST and OP/SYRTE, none being known to be extremely wreckless in this regard, to say the least. This is well understood techniques now, so that it matures into commercial products is not strange. It's worth noting that optically probed cesium also exists from Oscilloquartz, altering the beam standard techniques. Common to all three clocks is the fact that they use semiconductor lasers to pump and interact with the element, and therein lays also the challenge of having such laser-systems operating long-term. This is for sure the way forward, and these are just the for-runners of the continiously operating optical clocks that may one day become commercial products. So, while hydrogen masers may work and large cell rubidiums can be cleaned up, eventually we come to the point where these new techniques will take over for many good reasons. Maybe one day we will have time-nuts with cold rubidium clocks and maybe even optical clocks. Cheers, Magnus ___ 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] Cold Rubidium over hyped?
I think you are missing the key selling point of this device, namely it's long term stability and accuracy of a few parts in 10^15. From my point of view as a national timekeeper, this is much more useful than good short term stability. UTC reporting is at 5 day intervals so what the clock does at 1000 s is not so important. By the way, there is another comparison with 12 NIST masers in the current brochure: https://spectradynamics.com/product-sheets/cRb-Clock-2019.pdf There are evidently two models of maser here ,which politely, they do not identify. Cheers Michael On Sat, Nov 9, 2019 at 11:00 AM wrote: > > Well I have been looking at the data in the > > https://www.researchgate.net/publication/325499937_A_portable_cold_87_Rb_ > atomic_clock_with_frequency_instability_at_one_day_in_the_10-15_range > > link and find that maybe they are overstating their performance! > > In the plot of figure 5 my HP 5065A almost perfectly matches the Allan > deviation > out to 1000 Sec.! (Although mine does have VERY good performance) > > Also if you look at figure 7 all the Maser data shown seems to be from > poorly > operating Masers so any judgement of better clock performance versus the > Masers > is a bit much! > > The figure 5 data looks much better but still is not beating a good > active Maser. > > The EFOS2 a 1982 vintage Maser as well as the MHM 2010 and several other > modern Masers > I could find data for show between 2 and 5X10-15th at 1000 Sec. > The MHM 2010 specs at 5X10-15th at 100Sec and 2.0X10-15th at 1000Sec > All the Masers shown are worse than that spec! > Also my old Kvarz passive maser has 2x10-13th at 100 Sec just shy of > matching the top two Masers at 100Sec, which I don't believe! > > Something does not add up in their data! > > So I'm not really that impressed and would take an Active or Passive > Maser anyday. > > Just wonder if some 5065A can get so impressive that they don't just > make a modern large/cool cell classic Rubidium with modern electronics > technology! Certainly would be cheaper and more long lived also. > > Just my thoughts! > > Cheers, > > Corby > ___ > 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.
[time-nuts] Cold Rubidium over hyped?
Well I have been looking at the data in the https://www.researchgate.net/publication/325499937_A_portable_cold_87_Rb_ atomic_clock_with_frequency_instability_at_one_day_in_the_10-15_range link and find that maybe they are overstating their performance! In the plot of figure 5 my HP 5065A almost perfectly matches the Allan deviation out to 1000 Sec.! (Although mine does have VERY good performance) Also if you look at figure 7 all the Maser data shown seems to be from poorly operating Masers so any judgement of better clock performance versus the Masers is a bit much! The figure 5 data looks much better but still is not beating a good active Maser. The EFOS2 a 1982 vintage Maser as well as the MHM 2010 and several other modern Masers I could find data for show between 2 and 5X10-15th at 1000 Sec. The MHM 2010 specs at 5X10-15th at 100Sec and 2.0X10-15th at 1000Sec All the Masers shown are worse than that spec! Also my old Kvarz passive maser has 2x10-13th at 100 Sec just shy of matching the top two Masers at 100Sec, which I don't believe! Something does not add up in their data! So I'm not really that impressed and would take an Active or Passive Maser anyday. Just wonder if some 5065A can get so impressive that they don't just make a modern large/cool cell classic Rubidium with modern electronics technology! Certainly would be cheaper and more long lived also. Just my thoughts! Cheers, Corby ___ 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.
