  We demonstrate that any pure bipartite state of two qubits may be decomposed
into a superposition of a maximally entangled state and an orthogonal
factorizable one. Although there are many such decompositions, the weights of
the two superposed states are, remarkably, unique. We propose a measure of
entanglement based on this decomposition. We also demonstrate that this measure
is connected to three measures of entanglement previously set forth: maximal
violation of Bell's inequality, concurrence, and two-particle visibility.
