[time-nuts] Is 5061A by itself a primary reference? Was: Modern Rb atomic reference vs classic Cs

[Richard (Rick) Karlquist]

On 3/14/2020 1:57 PM, Hal Murray wrote:
> 
> richard at karlquist.com said:
>> At one time, only cesium standards were considered truly primary because of
>> the definition of the second.  However, the quantum mechanical constants of
>> other atoms such as Rb have been measured to much more accuracy than the 5071
>> so that Rb standards can be considered traceable to Cs if they are otherwise
>> of primary architecture.  The key idea is that all Rb atoms are absolutely
>> identical.  Rb gas cells are of course never primary.
> 
> Can the physics-nuts calculate the Rb frequency relative to Cs?

I used to wonder about why there isn't a formula for calculating
the transition frequencies for an atom, at least relative to
another variety, but I know almost nothing about quantum mechanics.
Evidently, if it were possible, we would have heard about it by now.

> 
> What's missing on a gas cell?  Is the problem theory or implementation?
> 

The buffer gas shifts the frequency depending on pressure and 
temperature.  There apparently isn't any reasonable way to sense
the pressure in the cell.  Also, there is "light shift" that can't
be eliminated, etc.  When I worked on the HP 10816 40 years ago,
there was "power shift" from the RF.  There may be a way now to
finesse that away.  Anyway, theory doesn't support the idea
that it's just implementation that is the panacea.

As far as implementation goes, that depends on suitable lasers,
which weren't around in those days.   Even then, you have doppler
shift, unless you use cold atoms.  Etc.

Rick N6RK