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

[Tom Van Baak]

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/


 > 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


 > 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.

/tvb

On 12/8/2019 1:45 PM, Magnus Danielson wrote:
> Hi,
>
> On 2019-12-07 21:46, Anders Wallin wrote:
>> In Cs my understanding is that a transition mF=0 to mF=0 transition is used
>> - so it is insensitive to the magnetic field[1].
>> There is no magnetic field insensitive component of the 88Sr+ clock
>> transition (other optical clocks will vary!)
>> See e.g. around page 10 here for an energy-level diagram:
>> http://resource.npl.co.uk/docs/networks/time/meeting3/klein.pdf
> Let me make a somewhat more accurate model.
>
> 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. 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. 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.
>
> Later the +1 and -1 transitions with their much stronger dependence on
> the magnetic field, as being measured can be used to servo the magnetic
> field to lock the +1 to -1 difference and with that the magnetic field
> is stabilized and the offset caused by the magnetic field on the 0
> transition used for clock steering and then it starts to approach real
> primary clock behavior.
>
> So, insensitive is overstating it, more much less sensitivity than the
> other transitions, but the details of them is very useful. At some time
> I should re-read it to learn these things deeper.
>
>> To measure 88Sr+ line-center (where there is no peak at nonzero B-field!)
>> the mid-point between a Zeeman pair is a good approximation, but one gets
>> rid of the electric quadrupole shift by measuring the center of three pairs
>> of components and calculating line-center from that. The servo-loop will
>> thus need to probe the left and right side of multiple peaks in sequence.
>> Our pulse-sequence now does 100 probe-pulses in about 7 seconds. If we
>> probe left/right side of three pars (twelve frequencies in total) the
>> line-center can be computed about once per minute. The ultra-stable clock
>> laser acting as local oscillator needs to maintain stability on its own
>> during those 1-2 minutes.
>>
>> The BIPM SRS document has more references
>> https://www.bipm.org/utils/common/pdf/mep/88Sr+_445THz_2017.pdf
> Sounds like lots of fun and would be cool to see in reality. Thanks for
> the links.
>
> If one had time and resources... and spare cubic meters in the lab.
>
> Cheers,
> Magnus
>
>
>
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