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A model of quantum measurement is proposed, which aims to describestatistical mechanical aspects of this phenomenon, starting from a purelyHamiltonian formulation. The macroscopic measurement apparatus is modeled as anideal Bose gas, the order parameter of which, that is, the amplitude of thecondensate, is the pointer variable. It is shown that properties ofirreversibility and ergodicity breaking, which are inherent in the modelapparatus, ensure the appearance of definite results of the measurement, andprovide a dynamical realization of wave-function reduction or collapse. Themeasurement process takes place in two steps: First, the reduction of the stateof the tested system occurs over a time of order $\hbar/(TN^{1/4})$, where $T$is the temperature of the apparatus, and $N$ is the number of its degrees offreedom. This decoherence process is governed by the apparatus-systeminteraction. During the second step classical correlations are establishedbetween the apparatus and the tested system over the much longer time-scale ofequilibration of the apparatus. The influence of the parameters of the model onnon-ideality of the measurement is discussed. Schr\"{o}dinger kittens, EPRsetups and information transfer are analyzed.Comment: 35 pages revte

Quantum measurement as a driven phase transition: An exactly solvable model