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Quantum Teleportation

Quantum teleportation is a protocol that transfers an unknown quantum state from one qubit to another using shared entanglement and classical communication, without physically transmitting the qubit.

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What it means

Quantum teleportation, proposed by Bennett et al.in 1993, allows Alice to transfer an unknown quantum state |ψ⟩ to Bob using a pre-shared Bell pair and two classical bits of communication.The protocol consists of three steps: (1) Alice performs a Bell measurement on her unknown qubit and her half of the entangled pair, (2) she sends the two-bit measurement result to Bob via a classical channel, and (3) Bob applies the corresponding Pauli correction (I, X, Z, or XZ) to his half of the entangled pair, recovering the original state |ψ⟩.Crucially, the original state at Alice's location is destroyed in the process (satisfying no-cloning), and the quantum information cannot travel faster than light because the classical bits are required.

Everyday analogy

Quantum teleportation is like faxing a document where the original is shredded during transmission — the content arrives at the destination, but the original is destroyed, and you need both the fax line (entanglement) and a phone call (classical bits) to complete the transfer.
Think of two magic envelopes (entangled pair): when Alice writes her message by combining it with her envelope and then calls Bob with instructions, Bob can reconstruct the exact message using his envelope — but Alice's message is gone.

Common misconceptions

  • Quantum teleportation does NOT allow faster-than-light communication — classical communication is required to complete the protocol, which is limited to the speed of light.
  • Quantum teleportation does NOT transport matter or energy — it transfers only the quantum state (information) from one qubit to another.

Key takeaways

  • Quantum teleportation requires a shared entangled pair and two classical bits of communication.
  • The original state is destroyed during teleportation, consistent with the no-cloning theorem.
  • Teleportation is a key primitive in quantum networking, quantum error correction, and measurement-based quantum computing.

Check your understanding

How many classical bits must Alice send to Bob to complete quantum teleportation of one qubit?

  1. A.0
  2. B.1
  3. C.2
  4. D.3
Show the answer

Answer: C. 2

Why: Alice must send 2 classical bits encoding her Bell measurement result, which Bob uses to apply the correct Pauli correction to his qubit.

Builds on

QubitQuantum EntanglementBell StatesQuantum MeasurementCNOT Gate

Related concepts

SuperpositionPauli-X GateGHZ State

Primary source: Bennett et al., Teleporting an unknown quantum state via dual classical and Einstein-Podolsky-Rosen channels, Phys. Rev. Lett. 70, 1895 (1993), doi:10.1103/PhysRevLett.70.1895

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