This one is important and relatively clear. Think of it's implications if I turn out to be right that post-quantum entanglement signals exist when distinguishable non-orthogonal Glauber coherent sender states entangled with ordinary receiver qubits are used.
No Signalling and Quantum Key Distribution
Jonathan Barrett,1, 2, ? Lucien Hardy,3, † and Adrian Kent4, ‡
1Physique Th ?eorique, Universit ?e Libre de Bruxelles,
CP 225, Boulevard du Triomphe, 1050 Bruxelles, Belgium
2Centre for Quantum Information and Communication, CP 165/59, Universit ?e Libre de Bruxelles, Avenue F. D. Roosevelt 50, 1050 Bruxelles, Belgium 3Perimeter Institute, 35 King Street North, Waterloo ON, N2J 2W9, Canada 4Centre for Quantum Computation, DAMTP, Centre for Mathematical Sciences, University of Cambridge, Wilberforce Road, Cambridge CB3 0WA, U.K. (Dated: March 2005 (revised))
Standard quantum key distribution protocols are provably secure against eavesdropping attacks, if quantum theory is correct. It is theoretically interesting to know if we need to assume the validity of quantum theory to prove the security of quantum key distribution, or whether its security can be based on other physical principles. The question would also be of practical interest if quantum mechanics were ever to fail in some regime, because a scientifically and technologically advanced eavesdropper could perhaps use post-quantum physics to extract information from quantum communications without necessarily causing the quantum state disturbances on which existing security proofs rely. Here we describe a key distribution scheme provably secure against general attacks by a post-quantum eavesdropper who is limited only by the impossibility of superluminal signalling. The security of the scheme stems from violation of a Bell inequality.