Preferred states of the apparatus.

A simple one-dimensional model for the system-apparatus interaction is analysed. The system is a spin-1/2 particle, and its position and momentum degrees constitute the apparatus. An analysis involving only unitary Schrödinger dynamics illustrates the nature of the correlations established in the system-apparatus entangled state. It is shown that even in the absence of any environment-induced decoherence, or any other measurement model, certain initial states of the apparatus - like localized Gaussian wavepackets - are preferred over others, in terms of measurementlike one-to-one correlations in the pure system-apparatus entangled state. [ABSTRACT FROM AUTHOR]