Collapse of the Quantum Wavefunction

Abstract

We show using a realistic Hamiltonian-type model that definite outcomes of quantum measurements may emerge from quantum evolution of pure states, i.e quantum dynamics provides a deterministic collapse of the wavefunction in a quantum measurement process. The relaxation of the wavefunction into a pointer state with classical properties is driven by the interaction with an environment. The destruction of superpositions, i.e. choosing a preferred attraction basin and thereby a preferred pointer state, is caused by a tiny nonlinearity in the macroscopic measurement apparatus. In more details, we numerically studied the many-body quantum dynamics of a closed Universe consisting of a system spin measured by a ferromagnet embedded in a spin-glass environment. The nonlinear term is the self-induced magnetic field of the ferromagnet. The statistics for the outcomes of this quantum measurement process depends on the size of the attraction basins in the measurement apparatus and are in accordance to Born's rule.