Mixed-state entanglement and quantum teleportation through noisy channels

The quantum teleportation with a noisy EPR state is discussed. Using an optimal decomposition technique, we compute the concurrence, entanglement of formation and Groverian measure for various noisy EPR resources. It is shown analytically that all entanglement measures reduce to zero when (F) over bar <= 2/3, where (F) over bar is an average fidelity between Alice and Bob. This fact indicates that the entanglement is a genuine physical resource for the teleportation process. This fact gives valuable clues to the optimal decomposition for higher-qubit mixed states. As an example, the optimal decompositions for the 3-qubit mixed states are discussed by adopting a teleportation with a W-state.