[time-nuts] Cs tube pics

[Attila Kinali]

On Wed, 02 Nov 2016 10:02:53 +0000
"Poul-Henning Kamp" <phk at phk.freebsd.dk> wrote:

> In message <20161102104103.0c58d35a72b7b36253b3d6b2 at kinali.ch>, Attila Kinali writes:
> 
> >I still would like to try to build my own atomic clock at some point,
> >even if it would be a quite costly, and a many years project. 
> 
> If you like lasers, build an ion trap.
> 
> If you only like lasers a little bit, build an optically pumped standard.
> 
> If you *really* like lasers, build a fountain.

If you *really*really* like lasers build an neutral atom optical clock :-)

A fountain is a quite intricate design. Beside doing the MOT one needs
to launch the atoms in a precisely determined direction with precisely
controlled speed, such that they pass trough the cavity with a constant
timing. If multiple cavities are used, the alignment is sligtly more
difficult (not just launching straigth up, but in a parabola and mistakes
make the atoms get lost completely, and not just arrive early/late). 

It might be easier to just let the atoms fall freely within the cavity
and do the Ramsey probing using lasers instead of a microwave cavity. 
Of course this reduces the time avaible and induces a Doppler shift which
needs to be calculated and compensated.
 
> The one thing nobody has done or even tried yet, (as far as I know),
> is optically excite a solid crystal.

This has been done. Ok, not the whole crystal, but single atoms within
the crystall. The most popular is probably diamond nitrogen vacancy defects:

"Timekeeping with electron spin states in diamond", by Hodges, Yao,
Maclaurin, Rasogi, Lukin, Englund, 2013
http://link.aps.org/doi/10.1103/PhysRevA.87.032118
https://arxiv.org/abs/1109.3241

"Solid-state electronic spin coherence time approaching one second",
by Bar-Gill, Pham, Jarmola, Budker, Walsworth, 2013
http://dx.doi.org/10.1038/ncomms2771

"High-resolution correlation spectroscopy of 13C spins near a
nitrogen-vacancy centre in diamond", by Laraoui, Dolde, Burk, Reinhard,
Wrachtrup, Meriles, 2013, 
http://dx.doi.org/10.1038/ncomms2685 

But these all suffer from one problem: mounting and temperature effects.
Because the nitrogen atom is not in free space, but bond trough its
valence electrons to the surrounding carbon atoms, it is directly influenced
by them. Any change in distance or strain directly affects the energy levels.

			Attila Kinali

-- 
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
                 -- Miss Matheson, The Diamond Age, Neil Stephenson