The Quantum No-Stretching: A geometrical interpretation of the no-cloning theorem

We consider the ideal situation in which a space rotation is transferred from a quantum spin j to a quantum spin l different from j. Quantum-information theoretical considerations lead to the conclusion that such operation is possible only for lj. For l>j the optimal stretching transformation is derived. We show that for qubits the present no-stretching theorem is equivalent to the usual no-cloning theorem.