Generalized robustness of entanglement

The robustness of entanglement results of Vidal and Tarrach [Phys. Rev. A 59, 141 (1999)] considered the problem whereby an entangled state is mixed with a separable state so that the overall state becomes nonentangled. In general, it is known that there are also cases when entangled states are mixed with other entangled states and where the sum is separable. In this paper, we treat a more general case where entangled states can be mixed with any states so that the resulting mixture is unentangled. It is found that entangled pure states for this generalized case have the same robustness as the restricted case of Vidal and Tarrach.