  We introduce a weak form of the realignment separability criterion which is
particularly suited to detect continuous-variable entanglement and is
physically implementable (it requires linear optics transformations and
homodyne detection). Moreover, we define a family of states, called
Schmidt-symmetric states, for which the weak realignment criterion reduces to
the original formulation of the realignment criterion, making it even more
valuable as it is easily computable especially in higher dimensions. Then, we
focus in particular on Gaussian states and introduce a filtration procedure
based on noiseless amplification or attenuation, which enhances the
entanglement detection sensitivity. In some specific examples, it does even
better than the original realignment criterion.
