Note on Entanglement of an Arbitrary State of Two Qubits

It is shown that the norm of the polarization vector of the reduced density matrix can characterize the entanglement of two qubits and so it is defined as a simple measure of entanglement. It is then extended to the generalized entanglement of polarization vector. It is proved that the entanglement of formation belongs to the generalized entanglement of polarization vector. Under the local general measurement and classical communication how this generalized entanglement of polarization vector changes is proved strictly and so the first and second laws of quantum information processing are verified clearly.