[time-nuts] Yb clock - stability estimation procedure?

[Tom Van Baak]

Hi Frank,

Correct, there is the underlying assumption that common mode [frequency] drift isn't present. That's been true for Cs standards (and the definition of the SI second) as well. If you can't prove it wrong, at least you can try to measure the lower bounds of drift, if such drift does occur.

This is one reason why there have been so many clock comparisons the past decade. National labs love to compare clock type X against clock type Y to see if they can be the first to detect something strange in the universe. For example, it might be the case that hydrogen-based clocks drift at a different rate than Cs or Hg or Al or Ca or Yb, etc. Google for phrases like Fine Structure Constant Variation or Variations in Fundamental Constants. Some papers and talks to get you started:

Improved Limits on Variation of the Fine Structure Constant and Violation of Local Position Invariance
http://tf.nist.gov/general/pdf/2238.pdf

Laboratory Tests on Variations of Fundamental Constants
https://www.kvi.nl/ssp2012/material/36-peik/slides/36-1-SSP-Groningen-Peik-2.pdf

New limits on variation of the fine-structure constant using atomic dysprosium
http://arxiv.org/pdf/1304.6940v1.pdf

Searching for temporal variation of the fine-structure "constant" in radio-frequency transitions of Dy
http://www.int.washington.edu/talks/WorkShops/int_07_1/People/Budker_D/Budker.pdf

/tvb

----- Original Message ----- 
From: "Frank Stellmach" <frank.stellmach at freenet.de>
To: <time-nuts at febo.com>
Sent: Sunday, August 25, 2013 9:47 AM
Subject: [time-nuts] Yb clock - stability estimation procedure?


> Hello time-nuts,
> 
> The NIST paper describes the estimation of the stability of one Yb clock 
> by simply comparing two equivalent clocks, and dividing by sqrt(2).
> This is obviously a common Metrological Practise, every time if 
> "something better" is not existent or not available.
> 
> This practise can be found everywhere in metrology: the comparison of Cs 
> clocks of all National Metrological Institutes, the comparison of two 
> Josephson Junctions in situ, claiming 1e-19 stability, the comparison of 
> the old Weston Cells, comparison of the Primary Kilograms and stating a 
> deviation of 1e-8, and so on.
> 
> Those comparisons and stability estimations later become fixed 
> definitions of the new definition of the unit, accompanied by setting 
> the uncertainty to the stability estimation found before.
> 
> That means, the next definition of the second, based on the Yb optical 
> clock would be provided by a new value and definition for the frequency 
> of the optical excitation, with an uncertainty of something like 1e-18, 
> or the Allan deviation given in the paper.
> 
> 
> I wonder, what is the validity of this stability estimation, as the 
> number of the different standards is very limited, and as there's always 
> the probability, that two different clocks /standards may drift in the 
> same direction.
> 
> Also, there are always some physical effects left, which may (in alinear 
> manner) shift the realization of the unit, let it be the magnetic field 
> for a Cs clock, or an electrical filed for optical clocks.
> 
> Does anybody know, where I can find the suitable standardized 
> metrological regulation for that problem, i.e. under which circumstances 
> such a logical step from estimation to specification is valid, and the 
> associated statistical calculation framework?
> 
> 
> 
> I have naively transferred this procedure to my artefact standards, i.e. 
> 5 Vishay precision resistor , and 4 volt references.
> 
> As those groups have very small annual drift and as I don't see a 
> logical difference in comparison to the stability estimations of those 
> quantum references, I also claim the stability of each artefact to be in 
> the order of the found drift within the observed group.
> 
> Now I would like to know, if I have overlooked something, and how to 
> make a serious stability estimation by correct metrological/statistical 
> calculations.
> 
> 
> Thanks Frank
>