Operational measurements in quantum mechanics (Q1387180)

Since the pioneering works of \textit{G. Ludwig} [see, e.g. ``Foundations of quantum mechanics. I'' (Springer-Verlag, New York) (1983; Zbl 0509.46057)], \textit{E. B. Davies} [see, e.g., ``Quantum theory of open systems'' (Academic Press, London) (1976; Zbl 0388.46044)], and others in the late sixties and early seventies, much theoretical research has been done on quantum measurements and observables in the context of positive operator-valued measures. P. Kochański's and K. Wódkiewicz's paper represents a further contribution to that subject. After stating some general properties of quantum observables described by POV measures, the authors discuss two classes of examples. The first one concerns joint measurements of position and momentum as well as related measurements, the second one joint measurements of the components of an arbitrary spin \(s\). The paper provides an interesting review of results due to the authors and others; however, for a detailed exposition the reader is referred to some other articles. The introduction of the authors' term ``propensity'' for a probability density is unnecessary and, according to the reviewer's opinion, mildly exaggerated.