Limitations of Quantum Measurements I: Determination of the Minimal Amount of Non-Ideality and Identification of the Optimal Measuring Apparatuses

摘要

The problem of determining the minimal deviation from the ideal scheme in a measurement, compatible with the existence of additive conserved quantities, is reconsidered. In the case of the measurement of a spin component of a spin-1/2 particle, we rederive in a simple and rigorous way the bound previously obtained by Yanase. The procedure allows the derivation of definite equations characterizing an optimal measuring apparatus. A detailed discussion of the possible malfunctioning of the apparatuses is also given. (Atomindex citation 14:721210)