[time-nuts] GSP clock stabilitiy, Rb vs Cs

[Magnus Danielson]

On 05/06/2013 02:29 AM, Mike S wrote:
> On 5/4/2013 2:40 PM, Attila Kinali wrote:
>> Can anyone shed some light on why the GPS Cs beams have a worse stability
>> than the Rb vapor clocks?
>
> I don't know, but it makes me wonder about things like
>
> 1) How sensitive is each to C-field tuning - i.e. for the same change in
> C-field, by how much does each type change in relative frequency? (or
> maybe it's exactly the same, I know nothing about the Zeeman effect) I'd
> think there would be orbital changes in frequency, after all, it's
> orbiting a big magnet.

Rubidium is more sensitive to C-field than Caesium.

> 2) How tight a lock can be obtained on each? i.e. might the physical
> realizations of Rb clocks have a higher Q-factor?

The Q-value depends on the observation time, and for a Cs-beam this 
translates into beam-length assuming constant speed. Foutains has much 
better Q since they have longer observation time. H-masers started as a 
beam with a "bounce-box" to prolong the observation time.

Cheers,
Magnus