2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/114556We establish the non-existence of a universal Hadamard gate for arbitrary unknown qubits, by considering two different principles; namely, no-superluminal signalling and non-increase of entanglement under LOCC. It is also shown that these principles are not violated if and only if the qubit states are of a special form obtained in our recent work [ IJQI (in press), quant-ph/0505068 ].5 pages, LaTexQuantum Physicstext