  Entanglement detection and estimation are fundamental in quantum information
science. Compared with discrete-variable states, for which lots of efficient
entanglement detection criteria and lower bounds of entanglement measures have
been proposed, the continuous-variable entanglement is much less understood.
Here we shall present a family of entanglement witnesses based on
continuous-variable local orthogonal observables (CVLOOs) to detect and
estimate entanglement of Gaussian and non-Gaussian states, especially for bound
entangled states. By choosing an optimal set of CVLOOs our entanglement witness
is equivalent to the realignment criterion and can be used to detect bound
entanglement of a class of 2+2 mode Gaussian states. Via our entanglement
witness, lower bounds of two typical entanglement measures for arbitrary
two-mode continuous-variable states are obtained.
