My (poorly worded, convoluted and implicit) point was that propagation speed of an interaction is something we should be able to measure. Would you propose an experiment in which the decoherence propagation speed is measured?
There is no single universal rate at which decoherence propagates. The details will depend on the structure of the system and its environment. What we can say is that the speed of light sets an upper limit on the speed at which interactions can propagate, so decoherence will propagate at a finite rate.
As for measuring decoherence rates in specific cases, this has been done. Take this paper, for instance. The authors couple Be-9 ions prepared in superpositions of their energy eigenstates with various types of reservoirs, representing different environments....
Today's post, Spooky Action at a Distance: The No-Communication Theorem was originally published on 05 May 2008. A summary (taken from the LW wiki):
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