Degree Of Entanglement Of Werner States And Isotropic States Of Bsa

In this paper, at first we prove that the parameter obtained in an optimal decomposition of a state can be used as an entanglement measure, called BSA entanglement measure. This fact was proved by S. Karnas and M. Lewenstein in 2001. Here we present a more simple proof. Then we give the Lewenstein-Sanpera decompositions for Werner states and isotropic states, and obtain their BSA entanglement measure. Moreover, we compare the BSA entanglement measure for these two families of symmetric states with their other entanglement measures such as entanglement of formation, concurrence and tangle.