An argument for ψ-ontology in terms of protective measurements

•The ontological model framework is extended by including protective measurements.•ψ-Ontology is proved in this framework without relying on auxiliary assumptions.•The proof also applies to deterministic theories such as the de Broglie–Bohm theory.•A simpler argument for ψ-ontology is given based on a weaker criterion of reality.

The ontological model framework provides a rigorous approach to address the question of whether the quantum state is ontic or epistemic. When considering only conventional projective measurements, auxiliary assumptions are always needed to prove the reality of the quantum state in the framework. For example, the Pusey–Barrett–Rudolph theorem is based on an additional preparation independence assumption. In this paper, we give a new proof of ψ-ontology in terms of protective measurements in the ontological model framework. The proof does not rely on auxiliary assumptions, and it also applies to deterministic theories such as the de Broglie–Bohm theory. In addition, we give a simpler argument for ψ-ontology beyond the framework, which is based on protective measurements and a weaker criterion of reality. The argument may be also appealing for those people who favor an anti-realist view of quantum mechanics.