Minimum cbits for remote preperation and measurement of a qubit

Quantum teleportation requires 2 cbits to be sent from Alice to Bob in order to transmit an unknown qubit provided they share an entangled EPR pair. Classical teleportation requires 2.19 cbits to be sent from Alice to Bob in order to simulate a known qubit provided they share local hidden variables. We show that there is a simple scheme which requires 1 cbit to be sent from Alice to Bob for simulating a known qubit at a remote place provided they share an entangled EPR pair. This suggests that the classical teleportation should be compared with the present scheme for comparing the cbit cost (1.19 cbits more) and the use of entanglement versus local hidden variables. PACS NO: 03.67.-a, 03.65.Bz email:[email protected] The state of a quantum system contains a large amount of information which cannot be accessed by an observer. How well one can extract and utilise the largely inaccessible quantum information is the subject of quantum information theory. One of the surprising discoveries in this area is the teleportation of an unknown quantum state by Bennett et al [1] from one place to another without ever physically sending the particle. A qubit, for example, can be sent from Alice to Bob provided they share an EPR pair and Alice carries out a Bell-state measurement on the qubit and one half of the EPR pair, and sends 2 bits of classical information to Bob, who in turn can perform a unitary operation on his particle to get the original state. The quantum teleportation of photon has been demonstrated experimentally by Bouwmeester et al [2] and Boschi et al [3]. The continuous version of quantum teleportation has been also verified by Furusawa et al [4]. Though, a qubit contains a doubly infinity of bits of information, only 2 classical bits (cbits) are necessary to transmit a qubit in the teleportation process. This raises the question, whether it is really the minimum number of cbits needed to transmit a qubit. What about the rest of the infinity of this number of bits? It has been suggested that the remaining bits flow across the entanglement channel [5]. Is it that 2 cbits are required just to preserve the causality (the peaceful coexistence of quantum theory and relativity) or is it the “soul” of an unknown qubit (without