  Quantum teleportation is one of the essential primitives of quantum
communication. We suggest that any quantum teleportation scheme can be
characterized by its efficiency, i.e. how often it succeeds to teleport, its
fidelity, i.e. how well the input state is reproduced at the output, and by its
insensitivity to cross talk, i.e. how well it rejects an input state that is
not intended to teleport. We discuss these criteria for the two teleportation
experiments of independent qubits which have been performed thus far. In the
first experiment (Nature {\bf 390},575 (1997)) where the qubit states were
various different polarization states of photons, the fidelity of teleportation
was as high as 0.80 $\pm$ 0.05 thus clearly surpassing the limit of 2/3 which
can, in principle, be obtained by a direct measurement on the qubit and
classical communication. This high fidelity is confirmed in our second
experiment (Phys. Rev. Lett. {\bf 80}, 3891 (1998)), demonstrating entanglement
swapping, that is, realizing the teleportation of a qubit which itself is still
entangled to another one. This experiment is the only one up to date that
demonstrates the teleportation of a genuine unknown quantum state.
