Premeasurement vs. Measurement: A Basic Form of Complementarity

Traditionally, three forms of duality were found in quantum mechanics: between the wave–like and the corpuscular behaviour, between unitary dynamics and measurement, and between locality and non–locality. We show that connections between these three forms exist. Moreover, we point out that the fundamental duality of quantum mechanics, to which all the other ones can be led, is that between measurement and premeasurement, and develop a formalism in terms either of projectors or unitary transformations that can be used for both complementary features.