Abstract
The measuring process is an external intervention in the dynamics of a quantum system. It involves a unitary interaction of that system with a measuring apparatus, a further interaction of both with an unknown environment causing decoherence, and then the deletion of a subsystem. This description of the measuring process is a substantial generalization of current models in quantum measurement theory. In particular, no ancilla is needed. The final result is represented by a completely positive map of the quantum state (possibly with a change of the dimensions of A continuous limit of the above process leads to Lindblad’s equation for the quantum-dynamical semigroup [Commun. Math. Phys. 119 (1976)].
- Received 11 June 1999
DOI:https://doi.org/10.1103/PhysRevA.61.022116
©2000 American Physical Society