[ExI] Cramer on impossibility of FTL communication

Giulio Prisco giulio at gmail.com
Sun Aug 30 09:14:41 UTC 2015


Thanks for posting! By pure synchronicity, I was reading the paper
when your post arrived!

The consensus, even among imaginative mavericks like Cramer and
Herbert, seems to be that quantum entanglement can't be used for
instant messaging. That's kind of intuitive because measurements are
random anyway, entanglement or not, and cheating breaks the
entanglement. Of course one can hope to find a cleaver way of
cheating... Any news about that?

On Sun, Aug 30, 2015 at 10:19 AM, scerir at alice.it <scerir at alice.it> wrote:
> An Inquiry into the Possibility of Nonlocal Quantum Communication
>
> Authors:
> John G. Cramer,  Nick Herbert
>
> http://arxiv.org/abs/1409.5098
> Abstract:
> The possibility of nonlocal quantum
> communication is considered. We investigate three gedankenexperiments
> that have
> variable entanglement: (1) a 4-detector polarization-entangled system, (2) a 4-
> detector
> path-entangled system, and (3) a 3-detector path-entangled system
> that uses an innovative optical mixer
> to combine photon paths.
> A new quantum
> paradox is reviewed in which the presence or absence of an interference pattern
> in
> a path-entangled two photon system, controlled by measurement choice, is a
> potential nonlocal signal.
> We show that for the cases considered, even when
> interference patterns can be switched off and on,
> there is always a "signal"
> interference pattern and an "anti-signal" interference pattern that mask
> any
> observable interference when they are added, even when entanglement and
> coherence are
> simultaneously present. This behavior can be attributed to what
> in the literature has been called
> "the complementarity of one-particle and two-
> particle interference".
>
> Important papers about "the complementarity of one-
> particle and two-particle interference" are:
>
> http://arxiv.org/abs/quant-ph/0112065
> http://physics.gmu.edu/~rubinp/courses/123/superpositionprinciple.pdf
> That is
> to say it seems not possible to use quantum entanglement (i.e. two-photon
>
> position/momentum quantum entanglement) to create (or not) interference
> patterns
> on a screen (or whatever) at a distance.
>
> Of course we know there are
> theorems (i.e. by Ghirardi, etc.) showing we cannot use
> quantum entanglements
> for FTL communication. But we also know that theorems
> sometimes are circular.
> It is possible that formalisms used in this theorems
> (i.e. tensor product)
> already do not allow FTL communication (as pointed out by
> Kennedy)
>
> http://philpapers.org/rec/KENOTE
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