Entanglement degree measure and a criterion for sudden death as a phase transition in bipartite systems

We propose a method to compute the entanglement degree EE of bipartite systems having dimension 2 × 2 and demonstrate that the partial transposition of density matrix, the Peres criterion, arise as a consequence of our method. Differently from other existing measures of entanglement, the one presented here makes possible the derivation of a criterion to verify if an arbitrary bipartite entanglement will suffers sudden death (SD) based only on the initial-state parameters. Our method also makes possible to characterize the SD as a dynamical quantum phase transition, with order parameter EE, having a universal critical exponent −1/2.