Learning quantum mechanics entails adopting a new reference frame for the physical interpretation of the world. The quantum perspective is intrinsically connected with math, which becomes a sort of referent for physical meaning, requiring the employment of new formal structures and a new interpretation of familiar ones. Research evidences that students have difficulty both with concepts and with the use of formalism in qualitative tasks. We administered a 15-item questionnaire focused on incompatibility of observables and related formal structures to 40 physics students of three Italian universities. Semi-structured interviews were scheduled on a subset of students. Results concerning translation processes between math and physical meaning show that most students only look at the square modulus in order to reason on physical information encoded in quantum state, thus neglecting phase relations and their connection with incompatibility.
