Quantum teleportation
Quantum teleportation is a quantum information processing operation which can be summarized as follows:Suppose Alice and Bob (arbitrarily named protagonists) are spatially separated. They have at their disposition a classical information channel and share a perfectly entangled bipartite quantum state. Alice has a quantum system in a particular quantum state which she wishes to transfer to Bob. She does not know what the state is. Because measurements disturb quantum information, she cannot just measure her state and send the result to Bob over the channel. She could simply send him the system, but this involves the use of a quantum information channel which she may not have.
However, there is a method which allows her to transfer the state over to Bob by performing a manipulation involving her quantum system and her part of the shared entangled state, then sending 2 classical bits over the classical channel. Once Bob has received the information, he knows how to manipulate his part of the shared state in order to recover the unknown state at his location.
Alice's manipulation destroys her copy of the unknown state (if it did not, it would violate the no-cloning theorem). Note that despite appearances, this scheme could not be used for superluminal communication, because a classical information transfer is an integral part of the procedure.
The first experimental verification of the teleportation of the polarization state of a photon was reported in 1997. It is not clear if such a procedure can be scaled up to larger systems.
As quantum teleportation of the quantum state of a qubit was expected to be a key element in quantum computing, it might be significant that BARETT et al. report (Nature 429, 737 - 739 (17 June 2004)) "unconditional teleportation of massive particle qubits using atomic (9Be+) ions confined in a segmented ion trap, which aids individual qubit addressing. We achieve an average fidelity of 78 per cent, ...).
Teleporting an atom
The New York Times June 17, 2004 p.A21, reports that two teams, one from NIST, Boulder, Colorado, another from University of Innsbruck, Austria, have teleported atoms of beryllium and calcium, respectively, as published in Nature, June 17, 2004. The setup involves triplets of charged atoms (A, B, C) which are trapped in magnetic fields.
- B and C are entangled.
- C is moved away.
- B and A are entangled.
- The state of A and B are read, which affected C at a distance.
- When a pulse of laser light was aimed at C, then C was turned into an A (but which destroyed the A,B state, by the no-cloning theorem)