Sun, 21 Nov 1999 10:15:10 +0100
Stephen Paul King wrote:
> Hi All,
> Robert Fung is making some great points!
> ... entanglement is an additional problem when you consider
> not just the state-space of a single particle, but the
> state space of two particles that interacted and so their
> PD's and PDF's have some memory of that event as if they
> were two bell's (or impulse response functions) that
> once clanged together and when separated, they maintained
> a "memory" of that event in their separate sets of PDs and PDFs.
> Those separate memorys are what allow the two particles
> to be non-locally correlated, or "entangled".
> Those memories however tend fade away (decohere) after a while.
> But they should be maintainable, by a _local_ resonant
> communications between the entangled particles.
> Of what use that may be to quantum cryptography &c.,
> I am not concerned with, as I think there are more significant
> implications than that.
Decoherence is indeed a slippery concept, often used in an improper way.
The above statement about "fading memories" is in my opinion confusing.
The point is that decoherence does not destroy long-range quantum
superpositions. Decoherence just limits the ability of an observer
subject to the second principle of thermodynamics to keep track of such
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