[time-nuts] Cold Rubidium?

[Magnus Danielson]

Hi,

On 2019-10-27 10:12, Anders Wallin wrote:
> This paper from the french group has some details
> https://arxiv.org/pdf/1812.01658.pdf
> they say it's a redesign of the previous version (
> https://journals.aps.org/pra/abstract/10.1103/PhysRevA.82.033436), but it
> looks roughly the same..
> page 2 of the datasheet shows the vacuum system and bulb:
> https://www.muquans.com/wp-content/uploads/2019/03/muquans_muclock.pdf
>
> from what I understand in the French design the Ramsey interrogation is
> with a pulsed microwave source in the cavity.
> the fact that the atoms fall down during interrogation, when cooling is
> switched off, is not useful or significant at all(?)
> the US design is maybe more like a fountain with two interrogation-zones
> and the atoms fall through them?

You really want to avoid having two interrogation-zones as you can, and
this is one of the benefits of the fountain, since phase-errors causes a
frequency shift. The PTB cesium beams have beam-reversal which allows to
get the same effect in reverse and thus cancel.

Another problem with fountains is that the ball of atoms expands when
not under cooling, simply as effect of their remaining temperature. As
they then come back in they experience micro-lensing which then creates
a similar but smaller frequency shift, which can be calculated and
cancelled for which is done by most fountains.

I have not looked too deeply on the US one, but it seems to offer
interesting performance. It builds on a NIST project that was aimed for
Cesium and for space, but was repurposed for civilian use and rubidium.
I think the first ones are just delivered.

Cheers,
Magnus