Quantum cloning
= Quantum cloning
A cloning operation for a family of pure states would map
$$
|\psi\rangle|0\rangle\longmapsto|\psi\rangle|\psi\rangle
$$
for every state in that family. A single physical operation cannot clone every unknown quantum state.
The <no-cloning theorem> forbids a universal unknown-state cloning operation, while orthogonal families can be cloned.