ua nt - p h / 98 07 01 3 v 1 4 J ul 1 99 8 Experimental scheme for quantum teleportation of a single - photon packet

Both complete protocol and optical setup for experimental realization of quantum teleportation of unknown single-photon wave packet are proposed. Quantum mechanics prohibits cloning (copying) an unknown quantum state (no cloning theorem [1]). Is it possible to transmit to a distant user a previously unknown quantum state without sending that state itself? Strictly speaking, any measurement aimed at obtaining classical information to be sent to another observer changes the state itself without providing complete information about it. Production of a large number of identical copies which can be measured many times to obtain complete information on their common quantum state is prohibited by the no-cloning theorem. Thus, it is impossible to transmit information on a quantum state employing only a classical communication channel. Quantum teleportation lifts this restriction if a quantum communication channel is used in addition to the classical one. The idea of quantum teleportation for the case of discrete quantum states (e.g. a spin-1/2 particle in an unknown state) was first proposed in Ref.[3]. A quantum channel is realized through the non-local EPR-correlations [2,3] 1. An EPR-pair is a pair of particles described by an entangled state. Entanglement constitutes a special kind of quantum correlations which do not have any classical analogies. The quantum teleportation protocol described in Ref.[4] has the following form. To teleport an unknown quantum state from user A to a distant user B, user A generates an EPR-pair. One of the particles of that EPR-pair remains with the user A while the second one is sent to the distant user B. User A performs a joint measurement over the particle in the unknown state to be teleported and his particle from the EPR pair thus obtaining classical information. Because of the non-local correlations inherent in the EPR-pair, the measurement outcome uniquely determines the resulting state of the second particle in the EPR-pair sent to user B. The state of the second particle coincides with the unknown state to within a unitary rotation. Classical information obtained in the measurement is sent by user A to B and is used by the latter to determine which unitary transformation should be performed to obtain a new state identical to the original unknown state. In the course of teleportation user A obtains no information on the teleported unknown state. Quantum teleportation has recently been demonstrated experimentally for a photon in an unknown polarization state [5,6]. The problem of teleportation …