  An experimental success criterion for continuous-variable quantum
teleportation and memories is to surpass a limit of the average fidelity
achieved by the classical measure-and-prepare schemes with respect to a
Gaussian distributed set of coherent states. We present a simple proof of the
classical limit based on the familiar notions of the state-channel duality and
the partial transposition. The present method enables us to produce a
quantum-domain criterion associated with a given set of measured fidelities.
