Abstract

An unknown continuous-variable state can be teleported by use of the two-mode squeezed state as the quantum channel [1] If the quantum channel is maximally squeezed (100% squeezing), the unknown state will be perfectly reproduced at a remote place However the assumption of the maximally squeezed quantum channel is unphysical as it means the infinite average photon number of the channel state Moreover, the interaction of the channel state with the environment degrades the entanglement and purity of the channel We are interested in how the nonclassical features of the unknown state is revived by quantum teleportation in the real world It is obvious that a nonclassical nature in the unknown state can be lost during the teleportation even when the channel is entangled unless it is maximally entangled Is it also obvious that any nonclassical features cannot be teleported by a classically correlated channel? We find the relation between the entanglement of the channel and teleportation of nonclassical nature in the unknown state We are also interested in the fidelity of the teleportation, i e., the measure of how close the teleported state is to the original unknown state It is known that the quantum teleportation of a qubit (a two-level state) always gives a better fidelity than a classical teleportation [2] The fidelity for classical teleportation is obtained as we assume to extract optimal information from the original particle and send this information to prepare a particle at a remote place as close as the original one The classical average fidelity for the teleportation of a qubit is known to be 2/3, which is also the average fidelity of quantum teleportation when the channel loses its entanglement We study how to extract optimal information on a continuous-variable state to define the classical fidelity. We then compare the quantum and classical fidelities.

© 2000 IEEE