On Oct 18, 2015, at 5:50 PM, Magnus Danielson <mag...@rubidium.se> wrote:
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. Th
