An experiment that would measure noncommuting quantum-mechanical observables without collapsing the wave function has been recently proposed by Y. Aharonov, J. Anandan, and L. Vaidman [Phys. Rev. A 47, 4616 (1993)]. These authors argue that this ``protected measurement'' may give an indication on ``the reality of the wave function.'' We show that the proposed experiment admits a much simpler interpretation: it is an experiment in which the quantum system is (assumed to be) in an eigenstate of the observable being measured. As such, the fact that no collapse occurs is trivial and can be understood without the need of the concept of ``protective'' devices. We argue that the experiment does not provide a way for measuring noncommuting observables without a collapse, does not bear on the issue of the ``reality of the wave function,'' and does not add any particular insight into our understanding (or nonunderstanding) of quantum mechanics.
In a recent article Jan Sperling, Syamsundar De, Thomas Nitsche, Johannes Tiedau, Sonja Barkhofen, Benjamin Brecht, and Christine Silberhorn discuss the wave-particle duality using an experiment to demonstrate that "neither the wave nor the particle description is sufficient to predict the utcomes of quantum-optical experiments." I would like to draw your attention to two previous papers that discuss feasible experiments in which a photon does not seem to behave either as particle or as wave and make some brief considerations on the topic.