Quantum Nondemolition Measurements and the “Collapse” of the Wave Function
This book has dealt extensively with the interaction of optical apparatus with electromagnetic waves. With this background it is possible to analyze quantum measurements in the domain of optics. However, the point of view represented here is not confined to optics; it is an attempt to clarify some fundamental issues of the theory of quantum measurement. The interpretation of quantum measurements has long been the subject of controversy. The von Neumann postulate  “that the act of measurement projects the state of the observable into an eigenstate of the measurement apparatus” is a good working hypothesis for the interpretation of a quantum measurement. However, it has been criticized by Bell [9,185] as being an add-on to quantum theory, which describes the evolution of the states of physical observables by the Schrödinger equation. The “suddenness” of the collapse of the wave function into an eigenstate also contradicts physical intuition.
KeywordsDensity Matrix Coherent State Beam Splitter Probe Beam Measurement Apparatus
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