  An optical procedure in the context of continuous variables to verify
bipartite entanglement without destroying both systems and their entanglement
is proposed. To perform the nondestructive verification of entanglement, the
method relies on beam-splitter and quantum nondemolition (QND) interactions of
the signal modes with two ancillary probe modes. The probe modes are measured
by homodyne detections, and the obtained information is used to feed forward
modulation of signal modes, concluding the procedure. Characterizing the method
by figures of merit used in QND processes, we can establish the conditions for
an effectively quantum scheme. Based on such conditions, it is shown that the
classical information acquired from the homodyne detections of probe modes is
sufficient to verify the entanglement of the output signal modes. The
processing impact due to added noise on the output entanglement is assessed in
the case of Gaussian modes.
