The process of teleportation of a completely unknown single-photon relativi
stic state is considered. Analysis of the relativistic case reveals that th
e teleportation as it is understood in the non-relativistic quantum mechani
cs is impossible if no a priori information on the state to be teleported i
s available, It is only possible to speak of the amplitude of the propagati
on of the field (taking into account the measurement procedure) since the e
xistence of a common vacuum state together with the microcausality principl
e (the field operators commutation relations) make the concept of the propa
gation amplitude for the individual subsystems physically meaningless. When
partial a priori information is available (for example, only the polarizat
ion state of the photon is unknown while its spatial state is specified bef
orehand), the teleportation does become possible in the relativistic case.
In that case the a priori information can be used to "label" the identical
particles to make them effectively distinguishable. (C) 2000 Elsevier Scien
ce B.V. All rights reserved.