[time-nuts] CCTF Survey on redefinition of the Second and UTC

[Hal Murray]

This is from the time-zone list.
I dropped the HTML version and the PDF letter.
Archived version here:
  http://mm.icann.org/pipermail/tz/2021-January/029692.html

Survey here:
  https://www.surveymonkey.com/r/CCTF_Survey_2020
It has infoductory/background stuff that I haven't checked out yet.

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Subject: Re: [tz] CCTF survey on Time and Frequency Metrology - Telecom
From: "Gertsvolf, Marina" <Marina.Gertsvolf at nrc-cnrc.gc.ca>
Date: Tue, 12 Jan 2021 17:14:24 +0000
To: "Gertsvolf, Marina" <Marina.Gertsvolf at nrc-cnrc.gc.ca>
Cc: MILETI Gaetano <gaetano.mileti at unine.ch>,
        Frédéric Meynadier <Frederic.Meynadier at bipm.org>

Dear Colleague,

The last time the definition of the SI second was changed was in 1967 when =
Caesium atom hyperfine frequency transition was chosen as the reference val=
ue.

Since then first the primary thermal beam caesium clocks and then caesium f=
ountains have been providing the SI second realization values to steer the =
International Atomic Timescale. The current fountain uncertainties are at t=
he low 1E-16 level.

The frequency metrology research in recent years has surpassed the microwav=
e clocks, and optical frequency standards based on trapped ions and atoms n=
ow provide frequency measurements with evaluated uncertainties at the level=
 1E-18.

The frequency comparisons have also been advancing both through improved te=
chniques in Global Navigation Satellite Systems signal analysis and the Two=
 Way satellite Time and Frequency transfer as well as with fibre based freq=
uency links and portable optical clocks.
Frequency combs used to compare frequencies between clock lasers of differe=
nt optical clocks and also between optical frequencies and microwave 133Cs =
frequency of 9.192631770 GHz are now routine laboratory equipment and are c=
ommercially readily available.

These factors now provide a solid foundation to prepare for the redefinitio=
n of SI second based on the optical frequency standard. The exact approach =
is currently under discussion and it may be selecting one atomic candidate =
or building an ensemble. The specific requirements and the conditions for t=
he redefinition to take place are also being finalized.

The Consultative Committee for Time and Frequency (CCTF) has started prelim=
inary work on this subject, to investigate possible scenarios and their pos=
sible impact. It is within this framework that we contact you an expert in =
the field of Telecommunications, in order to make sure that the needs and w=
ishes of your community are integrated into the general debate that will ta=
ke place and may, eventually, lead to the redefinition of the second.

With the new definition, the frequency measurement accuracy will surpass th=
at of Caesium-based timescale by at least one order of magnitude and will p=
rovide an adequate tool for current and future research into fundamental ph=
ysics as well as technology exploitation.
The redefinition is not expected to affect any of the existing commercial f=
requency standard uncertainties such as those of caesium beam clocks or hyd=
rogen masers, because their uncertainties are generally orders of magnitude=
 higher than the expected accuracy of the new definition. Same is true for =
caesium fountains. The computation and dissemination of UTC will also not c=
hange, but UTC will become more stable and accurate based on the improved o=
ptical realizations of the SI second.

We would like to ask your expert opinion on whether the redefinition may ha=
ve any impact be it negative or positive on your field of study and operati=
on. The issues we would like you to consider are not just scientific and te=
chnological, but also regulatory and legislative. Your answers will be care=
fully examined and taken into account by CCTF in their analysis of Time and=
 Frequency metrology current and future needs and SI second and UTC evoluti=
on.


You can find the survey at https://www.surveymonkey.com/r/CCTF_Survey_2020 =
and in the attached letter from CCTF president No=EBl Dimarcq you will find=
 additional information on other activities at CCTF for your reference.


Best regards,
The CCTF Task Force on the redefinition of the second, subgroup A

Co-chairs:
Marina Gertsvolf (marina.gertsvolf at nrc-cnrc.gc.ca<mailto:marina.gertsvolf at n=
rc-cnrc.gc.ca>)
Gaetano Mileti (gaetano.mileti at unine.ch<mailto:gaetano.mileti at unine.ch>)

Secretary:
Frederic Meynadier(frederic.meynadier at bipm.org<mailto:frederic.meynadier at bi=
pm.org>)



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