  We present a method to test quantum behavior of quantum information
processing devices, such as quantum memories, teleportation devices, channels
and quantum key distribution protocols. The test of quantum behavior can be
phrased as the verification of effective entanglement. Necessary separability
criteria are formulated in terms of a matrix of expectation values in
conjunction with the partial transposition map. Our method is designed to
reduce the resources for entanglement verification. A particular protocol based
on coherent states and homodyne detection is used to illustrate the method. A
possible test for the quantum nature of memories using two non-orthogonal
signal states arises naturally. Furthermore, closer inspection of the
measurement process in terms of the Stokes operators reveals a security threat
for quantum key distribution involving phase reference beams.
