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Glossary

Quantum glossary

No-cloning theorem

There is no process that makes an independent copy of an arbitrary unknown quantum state.

It follows directly from the linearity of quantum mechanics. It is why quantum error correction must be cleverer than keeping backups, and why an eavesdropper on quantum key distribution cannot copy the qubits and pass them on undisturbed.

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Related terms

  • Quantum key distribution — Protocols such as BB84 that let two parties agree a secret key, with any eavesdropping revealed by the errors it causes.
  • Quantum error correction — Encoding quantum information redundantly so errors can be detected and fixed without measuring — and destroying — the data.