[time-nuts] 8th Symposium on Frequency Standards and Metrology

Magnus Danielson magnus at rubidium.se
Sun Oct 18 21:50:44 UTC 2015


Hi,

I thought a small report might be appreciated.

It's been a very intensive week. Fellow time-nuts Attila Kinali and 
Marek Peca attended. Attila and I hanged out with Florian Teply on 
Friday after the sessions.

Anyway, in a sense of impeccable humor, the host of the conferance, 
Fritz Riehle of PTB, had mounted a Black Forrest Coo-Coo clock on the 
wall of the seminar room. This interrupted the nice overlook that David 
Wineland (who got his Nobel price 2012) with amusement as result. I 
ended up using the Coo-Coo clock as alternative time reference during 
the seminar.

Among the interesting things said was that a group have now been formed 
to look at the redefinition of the SI second in terms of the optical 
clocks. The motivation is that since the last symposium, the optical 
clocks have now with margin surpassed the microwave clocks. By the look 
at the trend-curves, by the next symposium the distance should be 
significant. Regardless, if a redefinition is to be done, there is a lot 
of homework to be done before it can be settled and then we should 
expect performance to have improved significantly.

Looking at the presentations, several contenders was presented, and it 
is a wide range of approaches being done. Interesting is also how 
comparison between both different implementation of a particular 
transition but also between different transitions is done. Optical combs 
has become a valuable tool in wide use and optical resonators of various 
forms is used in combination to the various form of traps.
We see Sr, Yb, Al, Mg and Ca clocks being attempted and compared.

Numerous approaches to compare on distance was also presented, where PTB 
is mighty proud of their new link which has a trend-line for 1E-19 
downto 1E-19 in the modified Allan deviation plot. I naturally spotted 
some systematics there, but they have good margin for the current 
clocks, so it is impressive as it is. They have changed the laser 
amplification method from EDFA to fiber-based, and their pump-lasers is 
being locked too. The amplifier is a bit narrow-band, but does not look 
to dominate the properties, so they are fine for now.

PTB and SYRTE have now a link between them to allow for comparison of 
their clocks, and the NPL - SYRTE link will soon be completed. More 
links in France is on-going as well as the link to INRIM. The SP - MIKES 
link was listed also.

Several improvements in satellite two-way methods was also shown, and 
people have already done test to compare optical clocks over existing 
methods (which is limited by todays standard) but the new links coming 
looks really promising for international comparison.

It was also interesting to see the presentation on cryogenic sapphire 
whispering gallery oscillators.

One interesting project is what they call "NIST on a chip" which 
attempts to provide not only frequency but several other units in form 
of a chip-scale device. So, they are looking wider on how frequency can 
be used in small form-factor, which will be of interest for length, 
current, voltage etc.

Several groups have been looking at modified Ramsey interrogation by 
applying a modified pulse-mechanism that helps to reduce the first 
degree light shift. This new scheme is called hyper Ramsey interrogation 
scheme. Another interesting technique being discussed was the 
spin-squeezing, which promised an improvement in 20 dB.

Several presentations where on the topic of optical line measuring which 
may not be of interest for clock transitions, but oh did the methods 
being used share similarities!

One presentation was on the use of GPS satellites on detecting Dark 
Matter. That guy ended up sharing lunch with us, and I think Marek and 
me answered some of the questions he had about satellites and their 
signals that he needed for his research. That we just "happen" to know 
this, is another thing. :)

The breakfast, coffee breaks, lunches, poster sessions and dinners as 
well as late night sessions all had lovely discussions. Phase noise, 
cross-correlation issues and delta-counters effect on ADEV was among the 
issues that came up regularly. Great fun with old and new friends.

I concluded that I have at least 3 papers to write as a consequence of 
this trip.

NIST presented the work on chip scale clocks they are working on, and 
one of their uses is in magnetic sensors. This had led them to test it 
in PTBs lab for biosignals. PTB has built a room which is very very 
quiet in terms of magnetic fields, so quiet in fact that it is the 
magnetically quietest place in the solar system. Attila and me naturally 
took the opportunity to visit this lab, as it was located relatively 
central in Berlin. The building starts of with an EMC shield, and then 
have large coils that not only cancels the earths magnetic field, but 
also the fluctuations. Then they had built a room which has 7 layers of 
mu-metal, really built as a box-in-a-box-in-a... and the door is an 
interesting object in itself, as it slide sideways and connect all 7 
layers at the same time. It took them 4 years to master the 
demagnetization of the mu-metal, and it has been operational for 10 
years now. Proud by friendly techs showed us what it can do and how it 
reacts. Very cool indeed. They should be proud, it's an achievement. I 
made the comparison to the things we do in atomic clocks.
They now have funding for an 8th layer of mu-metal to make the field 
even more homogenic. Oh, the lights in there where optical bent pipes. :)

In all, quite an experience.

So, the field is moving, things are happening, it is quite interesting 
future.

When I woke up at the hotel Saturday, all but one was gone. Strange 
feeling, but I then got to meet a friend who now lives in Berlin, and 
that warmed me up again. :)

Cheers,
Magnus

On 10/09/2015 08:54 PM, Magnus Danielson wrote:
> Fellow time-nuts,
>
> Next week is filled with interesting stuff as we gather in Potsdam for
> this:
>
> https://www.ptb.de/8fsm2015/about-the-symposium/
>
> I and Attila will be there, so who will join us?
>
> PS. For the moment I actually don't know how many Cs-clocks I have...
> it's complicated.
>
> Cheers,
> Magnus



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