We investigate statistics of matrix elements of observables, calculated in an eigenbasis of a quantum-mechanical evolution operator corresponding to a classically chaotic system. We propose a criterion that allows one to predict whether or not such statistics are faithful to random-matrix theory and define a random operator with respect to a given system.

• Received 2 November 1990

DOI:https://doi.org/10.1103/PhysRevA.44.956