Quantum Teleportation

Quantum teleportation is a protocol for transmitting a quantum state from one location to another without physically moving the particle that carries it. The transmission requires two classical resources: a shared pair of entangled particles and a classical communication channel. Quantum teleportation is not faster-than-light communication: the classical channel is necessary to complete the protocol, and no information about the teleported state travels faster than light.

The protocol, proposed by Bennett et al. in 1993, works as follows. Alice has a particle in an unknown quantum state. She and Bob share an entangled pair. Alice performs a joint measurement on her unknown particle and her half of the entangled pair, obtaining one of four possible outcomes. She sends this classical result (two bits) to Bob. Bob applies a corresponding unitary transformation to his half of the entangled pair, and the result is that his particle is now in the original unknown state.

The state has been destroyed at Alice's location and reconstructed at Bob's. The no-cloning theorem is respected: the original state is not duplicated. The entangled pair is consumed in the process. What has been transmitted is not matter or energy but quantum information — the exact coefficients of the superposition.

Quantum teleportation has been demonstrated experimentally with photons, ions, and superconducting qubits over distances ranging from meters to over a thousand kilometers (via satellite, by the Chinese Micius experiment). It is a building block for quantum computing architectures that require qubit transport and for quantum communication networks that distribute entanglement for cryptographic and computational purposes.