Do you have a reference to the UV transitions? I'm sure the LIGO folks think of themselves as being in a race with advancing clock technology with regards to actually detecting gravity waves.
I could not find many references, but I think clocks mainly make the instrument cheaper, or possible in the case of long-baseline satellite instruments.
http://www.thorium.at/?page_id=4
I could not find many references, but I think clocks mainly make the instrument cheaper, or possible in the case of long-baseline satellite instruments.