Information properties of generalised quantum measurements

The concept of generalised quantum measurement is introduced as a transformation establishing the correspondence between the initial state of an object and the final state of the object–instrument system with the help of a classical information index one-to-one related to a classically compatible set of the states of the object–instrument system. It is shown that this measurement includes all the types of measurements: standard projective, entangling, soft, and generalised measurements with a partial or complete dest-ruction of the initial information contained in the object. A special class of partially destructing measurements is considered which establish the correspondence between a continual set of states of finite-dimensional quantum systems and systems with an infinite-dimensional space of states. The information sense of these measurements is discussed and some information characteristics are calculated.