Quantum Teleportation
Teleportation transfers an unknown qubit state using a shared entangled pair and two classical bits, without moving the qubit itself.
Moving a state, not matter
Quantum teleportation transmits an unknown qubit state from one location to another using a pre-shared entangled pair and a two-bit classical message. Nothing physical travels; the state is reconstructed at the far end. It respects the no-cloning theorem because the original is destroyed in the process.
The protocol
- Alice and Bob share a Bell pair, one qubit each
- Alice has an unknown state |psi> to send
- Alice performs a joint Bell measurement on |psi> and her half of the pair
- She sends the two classical outcome bits to Bob
- Bob applies one of four corrections (I, X, Z, or XZ) to recover |psi>
Why classical bits are needed
Alice's Bell measurement yields one of four random results, each leaving Bob's qubit in a state related to |psi> by a known Pauli. Bob cannot know which correction to apply until Alice tells him her two bits. This is why teleportation cannot beat the speed of light: the classical message is essential and travels no faster than light.
Consistency with no-cloning
The original |psi> is destroyed by Alice's measurement, so at no point do two copies exist. Teleportation moves the state; it does not duplicate it. This is exactly what no-cloning permits — transfer with destruction is allowed, copying is not.
Why it matters
Teleportation is a building block, not a transporter for objects. It underlies quantum repeaters that extend entanglement over long distances, gate teleportation in fault-tolerant architectures, and the movement of logical qubits inside error-corrected machines. It shows that entanglement plus classical communication can accomplish tasks impossible with either alone.