Proof that FTL communication quantum protocol is impossible?

[Euclid's rat]

Hi all,

I am reading pretty much everywhere that no quantum protocol for faster-than-light communication can exist.

Now, clearly neither super-dense coding nor any other quantum protocol I know of can be used for FTL communication - but is there a self-contained proof that no such protocol can exist? And if yes, where can I find it?

I am asking this because last week I had to prove, for one of my courses, that a certain problem can not be solved by any quantum algorithm: I managed to prove that if the problem had a solution then FTL communication would be possible, and therefore I concluded that no algorithm could solve the problem.

I also found -and included in my homework- a different proof of the same result by means of the no-deleting theorem, but it was definitely clunkier and less elegant than my first one.

So, I ended up using both proofs, and justifying the first one by saying that FTL communication (and hence, the original problem) can not be performed because, in a relativistic framework, it would lead to violations of the principle of causality.

But I wonder if a direct proof of the impossibility of using EPR pairs to transmit information without physical carriers exists - I just started taking an interest in quantum information theory, and for all I know there could be a fairly well-known theorem stating exactly this

 

[DrChinese]

Welcome to PhysicsForums!

PhysicsForums member Vanesch has written up something proving this:

EPR, Density Matrices and FTL Signalling

This is a pdf file. I hope this helps.

 

[setAI]

no nonlocal information in true quantum systems:

http://arxiv.org/abs/quant-ph/9906007

http://arxiv.org/abs/quant-ph/0003146

 

[Euclid's rat]

Thank you for the references!