  We introduce a simple and efficient technique to verify quantum discord in
unknown Gaussian states and a certain class of non-Gaussian states. We show
that any separation in the peaks of the marginal distributions of one subsystem
conditioned on two different outcomes of homodyne measurements performed on the
other subsystem indicates correlation between the corresponding quadratures,
and hence nonzero discord. We also apply this method to non-Gaussian states
that are prepared by overlapping a statistical mixture of coherent and vacuum
states on a beam splitter. We experimentally demonstrate this technique by
verifying nonzero quantum discord in a bipartite Gaussian and certain class of
non-Gaussian states.
