Mechanisms of the wave-packet collapse and macroscopic limits in the quantum theory of measurement

Abstract

Mechanisms of the wave-packet collapse are studied by using the density matrix with the internal trace for detector variables. It is clarified that the simultaneous realization of the wave-packet collapse and the macroscopic property of the measured physical quantity in a macroscopic limit is important. It is also pointed out that another type of wave-packet collapse is possibly derived by the effect arising from the ambiguity involved in the initial state of the detector. This type of collapse does not describe the measurement process. However, this effect is unavoidable and derives the unsharpness of the experimental results in all measurements, then it is important in the precise analysis of the experimental results. The discrepancy of these effects from the real wave-packet collapse will be seen in the temperature dependence of measured quantities.