Local and nonlocal properties of Werner states

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Abstract
We consider a special kind of mixed states—a Werner derivative, which is the state transformed by nonlocal unitary—local or nonlocal—operations from a Werner state. We show the following: (i) The amount of entanglement of Werner derivatives cannot exceed that of the original Werner state. (ii) Although it is generally possible to increase the entanglement of a single copy of a Werner derivative by local quantum operations and classical communication, the maximal possible entanglement cannot exceed the entanglement of the original Werner state. The extractable entanglement of Werner derivatives is limited by the entanglement of the original Werner state.
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