Research on university student understanding of quantum mechanics (QM) has shown the fragmented nature of student mental models and the existence of deep and persistent difficulties to make sense of quantum formalism. Learning problems are often tied to a lack of recognition or misinterpretation of physical meaning of theoretical entities, especially of quantum state formal representation. Nevertheless there hasn't been much research on ideas ascribed by student to basic properties of state vector and wave function (WF), to their role in the theory and to their physical meaning. In order to explore student way of thinking and connections they make between formalism and concepts, we elaborated a questionnaire and an interview protocol. As research calibration stage, a case study was designed including a written questionnaire followed by semi-structured interviews to be administered to 3rd year physics students who are being exposed to QM university course. On the base of case study results, a structured questionnaire is designed to explore how students link quantum formalism to concepts both in general terms and in the application context of specific problems. A grid for a multiple perspectives exploration of ideas is the basis of the 21 items on three levels: cultural, qualitative-conceptual and formal. For each element of the grid, one or more items are designed in order to cross investigate the selected aspects.
