A Note on the Entropy of Entanglement and Entanglement Swapping Bounds

Abstract

Using the information content of correlations between multipartite systems, together with the notion of partitioning, we show that some general results about the evolution of correlations in quantum systems can be derived with only elementary methods. In particular, we show that for 2 quantum systems A and B, each comprised of a number of sub-systems, in which a partition of A interacts unitarily with a partition of B, then the total correlation can only increase (or remain unchanged) and is given simply by the sum of the initial correlation and the correlation that develops as a result of the interaction. We then show that in a 4 qubit entanglement swapping process the transferred degree of entanglement is bounded by the lower of the initial degrees of entanglements of the qubits.