Epsilon-measures of entanglement

We associate to every entanglement measure a family of measures which depend on a precision parameter, and which we call e-measures of entanglement. Their definition aims at addressing a realistic scenario in which we need to estimate the amount of entanglement in a state that is only partially known. We show that many properties of the original measure are inherited by the family, in particular weak monotonicity under transformations applied by means of local operations and classical communication (LOCC). On the other hand, they may increase on average under stochastic LOCC. Remarkably, the e-version of a convex entanglement measure is continuous even if the original entanglement measure is not, so that the e-version of an entanglement measure may be actually considered a smoothed version of it.