The Newton–Wigner position operators x 1, x 2, x 3, are the premier notion of position in relativistic quantum mechanics of a single particle. They enjoy the same commutation relations with the 3 space momentum operators and transform under rotations in the same way as the x, y, z in ordinary QM. Though formally they have the same properties with respect to p 1, p 2, p 3, as the position in ordinary QM, they have additional properties: One of these is that