Entanglement cost of mixed states

Abstract

We compute the entanglement cost of several families of bipartite mixed states, including arbitrary mixtures of two Bell states. This is achieved by developing a technique that allows us to ascertain the additivity of the entanglement of formation for any state supported on specific subspaces. As a side result, the proof of the irreversibility in asymptotic local manipulations of entanglement is extended to two-qubit systems.

4 pages, no figures, (v4) new results, including a new method to determine E_c for more general mixed states, presentation changed significantly