Criteria for continuous-variable quantum teleportation

We derive an experimentally testable criterion for the teleportation of qua ntum states of continuous variables. This criterion is especially relevant to the recent experiment of Furusawa et al. where an input-output fidelity of 0.58 +/- 0.02 was achieved for optical coherent stages. Our derivation d emonstrates that fidelities greater than 1/2 could not have been achieved t hrough the use of a classical channel alone; quantum entanglement was a cru cial ingredient in the experiment.