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Glossary

Quantum glossary

No-communication theorem

Also: no signalling, faster than light

Entanglement cannot be used to send information: nothing done to one half changes the statistics seen at the other.

Correlations only show up when the two parties compare results over an ordinary channel. This is why teleportation needs two classical bits per qubit, and why entanglement does not beat the speed of light.

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Related terms

  • Entanglement — A correlation between quantum systems so strong that the whole has a definite state while the parts do not.
  • Quantum teleportation — Transferring an unknown qubit state using a shared Bell pair plus two classical bits.