Quantum copying: Beyond the no-cloning theorem.

  title={Quantum copying: Beyond the no-cloning theorem.},
  author={Buzek and Hillery},
  journal={Physical review. A, Atomic, molecular, and optical physics},
  volume={54 3},
  • Buzek, Hillery
  • Published 20 July 1996
  • Physics
  • Physical review. A, Atomic, molecular, and optical physics
We analyze the possibility of copying ~that is, cloning! arbitrary states of a quantum-mechanical spin-1/2 system. We show that there exists a ‘‘universal quantum-copying machine’’ ~i.e., transformation! which approximately copies quantum-mechanical states such that the quality of its output does not depend on the input. We also examine a machine which combines a unitary transformation and a selective measurement to produce good copies of states in the neighborhood of a particular state. We… 
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