ar X iv : 0 90 9 . 02 95 v 1 [ qu an t - ph ] 2 S ep 2 00 9 1 Quantum weak values are not unique What do they actually measure ?

Precise definitions of “weak [quantum] measurements” and “weak value” [of a quantum observable] are offered, which seem to capture the meaning of the often vague ways that these terms are used in the literature. Simple finite dimensional examples are given showing that weak values are not unique. They therefore cannot correspond to any physical attribute of the system being “weakly” measured, contrary to impressions given by most of the literature on weak measurements.