Quantum system lifetimes and measurement perturbations

The contradiction between the classical interpretation of the decay of unstable states and its quantum description is considered. Model calculations for the observed lifetime are carried out based on the ''retarded reductions''. This assumption is a generalization of the recently proposed description of quantum system decay in terms of repeated measurement perturbations, taking into account that a measurement may not reduce the system to an unique state to a modified one. The exponential decay law is verified again. A modified equation giving the observed lifetime in terms of unperturbed quantum decay law, measurement frequency and reduction law is derived. It predicts deviation of the observed lifetime from the unperturbed one, together with a dependence on experimental procedures. The influence of different model unperturbed decay law and reduction laws on this effect is studied