Limitations on quantum measurements. II. Analysis of a model example

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Abstract
A solvable model of an apparatus for measuring a spin component of a spin-1/2 particle is considered. The model enjoys full rotational invariance and, in the limit case in which a part of the apparatus becomes infinitely massive, works according to the ideal measurement scheme. The model is applied to the study of the deviations from the ideal measurement scheme imposed by the conservation of angular momentum. The detailed analysis of the model allows one to calculate the size of the various nonideal terms in the measurement scheme and to understand the physical mechanism which gives rise to such terms.