The [[No-Cloning Theorem|no-cloning theorem]] states the impossibility to copy arbitrary [[Quantum State|quantum states]]. The *quantum teleportation protocol* makes it possible to send a quantum state from one party, [[Alice and Bob|Alice]], to another party, [[Alice and Bob|Bob]]. The protocol needs in total three [[Qubit|qubits]]: two on Alice's side and one on Bob's side. ![[quantum_teleportation.excalidraw.light.svg]] The goal is to transfer the state of Alice's first qubit (blue) to Bob's qubit. The quantum teleportation needs two main ingredients for that: [[Entanglement|entanglement]] between Alice's second qubit and Bob's qubit (orange) and a classical connection. The idea of the protocol is to entangle Alice's two qubits and modify Bob's state during the process. By measuring the two qubits on Alice's side, we can obtain the necessary information for a correction that we need to apply to the state on Bob's side. There are a couple of important observations to make 1. The *quantum teleportation protocol* does **not** teleport the [[Physical Qubit|physical qubit]], but just the [[Quantum Information|quantum information]] stored on Alice's first qubit. There is no matter being moved during the protocol. In this sense, *quantum teleportation* has very little to do with teleportation from science fiction movies. 2. *Quantum teleportation* does not transmit any information faster than light, i.e. it does not contradict [[Special Relativity|special relativity]]. The classical connection between Alice and Bob is paramount to ensure the correct quantum information arrived at Bot's side. 3. The measurement contains no information about the state being sent. It only contains information about the correction. There is nothing that anyone can intercept and given an entangled state to start with, teleportation is a completely secure communication protocol. >[!read]- Further Reading >- [[No-Cloning Theorem]] >- [[Entanglement]] >[!ref]- References > - C. H. Bennett, G. Brassard, C. Crépeau, R. Jozsa, A. Peres, and W. K. Wootters, Teleporting an unknown quantum state via dual classical and Einstein-Podolsky-Rosen channels, Phys. Rev. Lett. **70**, 1895 (1993).