Optimal Quantum Cloning Machines

  title={Optimal Quantum Cloning Machines},
  author={Nicolas Gisin and Serge Massar},
  journal={Physical Review Letters},
We present Quantum Cloning Machines (QCM) that transform N identical qubits into $M>N$ identical copies and we prove that the fidelity (quality) of these copies is optimal. The connection between cloning and measurement is discussed in detail. When the number of clones M tends towards infinity, the fidelity of each clone tends towards the optimal fidelity that can be obtained by a measurement on the input qubits. More generally, the QCM are universal devices to translate quantum information… 

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