Bound entanglement maximally violating Bell inequalities: quantum entanglement is not equivalent to quantum security

摘要

It is shown that Smolin four-qubit bound entangled states [Phys. Rev. A, 63032306 (2001)] can maximally violate two-setting Bell inequality similar tostandard CHSH inequality. Surprisingly this entanglement does not allow forsecure key distillation, so neither entanglement nor violation of Bellinequalities implies quantum security. It is also pointed out how that kind ofbound entanglement can be useful in reducing communication complexity.