  In contrast to discrete-variable teleportation, a quantum state is
imperfectly transferred from a sender to a remote receiver in a
continuous-variable setting. We recall the ingenious scheme proposed by
Braunstein and Kimble for teleporting a one-mode state of the quantum radiation
field. By analyzing this protocol, we have previously proven the factorization
of the characteristic function of the output state. This indicates that
teleportation is a noisy process that alters, to some extent, the input state.
Teleportation with a two-mode Gaussian EPR state can be described in terms of
the superposition of a distorting field with the input one. Here we analyze the
one-mode Gaussian distorting-field state. Some of its most important properties
are determined by the statistics of a positive EPR operator in the two-mode
Gaussian resource state. We finally examine the fidelity of teleportation of a
coherent state when using an arbitrary resource state.
