Superadditivity of two quantum information resources
Quantum entanglement leads to the most counterintuitive effects in physics and an important quantum resource which plays a central role in the field of quantum information and communication. Entanglement can be easily destroyed by the decoherence processes due to unwanted coupling with the environment. Such uncontrollable interaction introduces noise and transform for example maximally entangled states into mixed states. Therefore it is critical to know which mixed states can be distilled to maximally entangled states with the help of local operations and classical communication (LOCC) and then be valuable again for further information processing. It has been discovered that there is a new class of entangled states where no entanglement can be distilled and it has been called bound entanglement (BE) [1] After this discovery of bound entanglement, the impression was that this type of entanglement is completely useless for quantum information processing. However quickly it has been shown that even in bipartite case there is an option to pump entanglement of many bound entangled states into one weakly entangled pair to beat the quantum teleportation fidelity threshold unbeatable otherwise. This process is called activation of bound entanglement and it was the first manifestation of superadditivity of quantum communication resources [2]