  We consider the storage and transmission of a Gaussian distributed set of
coherent states of continuous variable systems. We prove a limit on the average
fidelity achievable when the states are transmitted or stored by a classical
channel, i.e., a measure and repreparation scheme which sends or stores
classical information only. The obtained bound is tight and serves as a
benchmark which has to be surpassed by quantum channels in order to outperform
any classical strategy. The success in experimental demonstrations of quantum
memories as well as quantum teleportation has to be judged on this footing.

Quantum Physics