An indirect measurement process parameterized by a nonunitary system–pointer interaction

An indirect quantum state measurement process is under investigation. Common evolution of the detector's microscopic part (pointer) and the measured system (target) is considered to be nonunitary due to the interaction between the pointer and the environment. The system of differential equations for superoperators, which map the initial target state into its conditional final state, is obtained. A developed formalism is applied to the problem of cavity quantum mode photodetection to investigate the basic information characteristics of this measurement process. (paper)