[time-nuts] Re: The SI second and the ease of realization (was: leap seconds finally being retired?)

[Magnus Danielson]

Hi Poul-Henning,

On 2022-11-25 22:47, Poul-Henning Kamp wrote:
> --------
> Magnus Danielson via time-nuts writes:
>
>> This however keep changing. We see how sub 1 ns is more reachable, and
>> 100 ps is closer to availabile with commercial needs. Optical frequency
>> comparison is regularly done with 1E-19 level of performance, [...]
> If optical clocks actually shone light, you could point the light
> from two of them at a screen, and use the resulting pattern of
> interference fringes to align them to the same exact height :-)
>
To within the precision of the realization, yes. It's done with counters 
and not interference patterns, in fact it is done with disimilar 
frequencies. The optical link is some suitable free 1550 nm range 
frequency which is tied to the optical transition usinga stable transfer 
laser and similarly in the other end. This is done using the optical 
combs to jump between frequencies and make comparisons using regular 
frequency counters.

It's just like the microwave mixing stuff but at higher frequencies.

Currently the leveling on dm level can be measured.

Cheers,
Magnus