Information Constraints in Quantum Measurements and State Collapse

Quantum-mechanical constraints on information transfer in measuring systems and their influence on measurement results studied. As the example, measurement of binary observable $S_z$ of object $\cal S$ by measuring apparatus $\cal A$ considered. It's shown that during the measurement these constraints obstacle the acquisition of information by $\cal A$, characterizing purity of $\cal S$ ensemble. Due to it, $\cal A$ can't discriminate pure and mixed $\cal S$ ensembles with the same $S_z$ expectation value. In algebraic measurement ansatz by Emch such information loss results in stochastic $S_z$ measurement outcomes for pure $\cal S$ ensemble, their probabilities obey to Born postulate, i.e. it corresponds to quantum state collapse. Account of $\cal A$ state decoherence doesn't change obtained results principally.