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QUANTUM MEASUREMENT

The basic results of the group in this subject are:

Luders change-of-state formula in ideal measurement rederived from the concept of minimal measurement. Equivalence of ideal and predictive measurement preserving sharp values of compatible observables.
The mixing character of a quantum state is strictly increasing in incomplete measurement. This points out the mixing character as as a refinement of the notion of entropy, yielding the factorization of the realistic quantum processes onto evolution and collapse.
A detailed study of Jauch's approach to the quantum theory of measurement was performed.
Retroactive apparent occurrence (RAO) of events in quantum mechanics is precisely defined. It enables to include the old intuitive idea of Niels Bohr ("Only a registered phenomenon is truly a phenomenon") into modern quantum theory of measurement. Also, RAO explaines the known delayed-choice experiments due to John Wheeler.
Classification of quantum measurements.
Evolution of the system during the continuous ideal measurement of an observable is described by the modified hamiltonian. Freezing of state (Zeno's paradox) is studied.

References:

F. Herbut,

Derivation of the change of state in measurement from the concept

of minimal measurement.

Annals of Physics 55 (1969) 271-300.

F. Herbut,

Minimal-disturbance measurement as a specification in von Neumann's

quantal theory of measurement.

International Journal of Theoretical Physics 11 (1974) 193-204.

F. Herbut and I.D. Ivanovic,

The principle of strictly increasing mixing character in incomplete

general measurement.