  Quantum entanglement is an enigmatic and powerful property that has attracted
much attention due to its usefulness in new ways of communications, like
quantum teleportation and quantum key distribution. Much effort has been done
to quantify entanglement. Indeed, there exist some well-established
separability criterion and analytical formulas for the entanglement of
bipartite systems. In some of these, the crucial elements are the eigenvalues
of the partial transpose of the density matrix. In this paper, we show that one
can also have information about the entanglement of bipartite state, in C2xC2,
looking at the minimal principals of the partial transpose.
