[time-nuts] 88Sr+ ion-clock live stream

[Magnus Danielson]

Tom,

On 2019-12-09 02:30, Tom Van Baak wrote:
> Magnus,
>
> > The mf values of +3, +2, +1, -1, -2, -3 transitions have a relatively
> > strong sensitivity to magnetic field, with a strong linear term on the
> > magnetic field strength, where as the 0 transition has a much weaker
> > quadratic sensitivity, assuming weak magnetic field which is fair
> > assumption.
>
> You can see this dramatically by turning the cfield adjustment from
> min to max:
>
> http://leapsecond.com/pages/cfield/
>
A good illustration of it, it does not show the fine-grained movement of
the 0 transition, because of the scale, but it is there.
>
> > This is true for any atomic transition, so it is not unique
> > to Cesium. Cesium has however the second weakest (of classical neutral
> > atom microwave frequency, only Thallium being better) magnetic
> > sensitivity for it's hyper-fine transition.
>
> Some late night reading about Thallium:
>
> 1957, Kusch
> "Precision Atomic Beam Techniques"
> https://ieeexplore.ieee.org/document/1536252
> kusch1957.pdf
>
> 1960, Mockler, Beehler, Snider
> "Atomic Beam Frequency Standards"
> http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.846.7115&rep=rep1&type=pdf
>
>
> 1963, Beehler, Glaze
> "Experimental Evaluation of a Thallium Beam Frequency Standard"
> https://tf.nist.gov/general/pdf/211.pdf
>
> 1966, Beehler, Glaze
> "Evaluation of a Thallium Atomic Beam Frequency Standard at the
> National Bureau of Standards"
> https://tf.nist.gov/general/pdf/9.pdf
>
> 1983, Ramsey
> "History of Atomic Clocks"
> https://tf.nist.gov/general/pdf/1916.pdf
> https://nvlpubs.nist.gov/nistpubs/jres/088/jresv88n5p301_A1b.pdf
>
>
Thanks for those links, I have read some of these, as one might have
guessed. With todays technology, we would have been more inclined to
Thallium of the two, as the two technological drawbacks of Thallium at
the time, the higher
> > Even with cesium, you can
> > tweak the frequency of transition with the change of the magnetic field
> > (B-field in the lingo). All such cesium clocks is really secondary
> > standards, even if marketing have been boasting their contribution a
> lot.
>
> Not sure what make/model cesium clock you're talking about here. Just
> because there are knobs to tweak doesn't demote them to secondary.

Just because you use the right atom and isotope does not give you a
primary standard. The clock build of analog cesiums (HP 5060A, 5061A/B
and 5062A to name a few) does not on their own balance their synthesis
chain to the shift that their open-loop magnetic field causes on the
cesium transition. This is comparable to the shift of the wall being
balanced by the buffert gases in a gas-cell such as rubidium (but lately
also cesium). Only the large laboratory cesium clocks was able to
self-calibrate the shift caused by magnetic field. Modern standards such
as FTS 4040, FTS 4065 and HP 5071A is able to servo the magnetic field
to balance it. The improved stability and accuracy is significant, but
for TAI purposes, that is not sufficient either, they are only used for
stability but not accurate observation of the SI transition.

So, we have some pretty darn cool toys, but primary references, well not
so much IMHO.

Cheers,
Magnus