  Protective measurements illustrate how Yakir Aharonov's fundamental insights
into quantum theory yield new experimental paradigms that allow us to test
quantum mechanics in ways that were not possible before. As for quantum theory
itself, protective measurements demonstrate that a quantum state describes a
single system, not only an ensemble of systems, and reveal a rich ontology in
the quantum state of a single system. We discuss in what sense protective
measurements anticipate the theorem of Pusey, Barrett, and Rudolph (PBR),
stating that, if quantum predictions are correct, then two distinct quantum
states cannot represent the same physical reality.
