In the paper by Kolovsky ( Europhys. Lett. , 27 (1994) 79) an equation for a mesoscopic particle, with internal structure, was proposed. Nevertheless, that equation is in confrontation with the stability of such a mesoscopic particle. This instability is independent of the chaotic character of the corresponding classical system.
The influence of quantum chaos on small atomic systems is reviewed. It now seems clear that chaos in the usually understood sense (e.g. exponential sensitivity to perturbations) is not found in isolated quantum systems. However, there are phenomena which appear only when the corresponding classical system is chaotic. The stability of the classical dynamics, in other words whether it is regular or chaotic, has a profound effect on the character of the corresponding quantum spectrum and wavefunctions.
The quantum dynamics of a classically chaotic model are studied in the approach to the macroscopic limit. The quantum predictions are compared and contrasted with the classical predictions of both Newtonian and Liouville mechanics. The time-domain scaling of the optimal quantum-classical correspondence is analyzed in detail in the case of both classical theories. In both cases the correspondence for observable quantities is shown to break down on a time-scale that increases very slowly (logarithmically) with increasing system size. In the case of quantum-Liouville correspondence such a short time-scale does not imply a breakdown of correspondence since the largest quantum-Liouville differences reached on this time-scale decrease rapidly (as an inverse power) with increasing system size. Therefore the statistical properties of chaotic dynamics are, as expected, well described by quantum theory in the macroscopic limit. In contrast, the largest quantum-Newtonian differences reached on the log time-scale actually increase in proportion to the system size. Since the invariance properties of the Hamiltonian impose functional constraints on the time-varying chaotic coordinates, it is possible to show, moreover, that if the quantum predictions are believed to describe the coordinates of individual chaotic systems, then they also predict macroscopic violations of any kinematic or dynamic constants of the motion. These results for chaotic systems indicate that a valid description of the time-varying properties of individual macroscopic bodies is not available within the standard interpretive framework of quantum theory.
We independently examine the case of a spin-j particle interacting with a boson field studied by Finney and Gea-Banacloche. We concentrate on their conclusion that in the case j=1/2 the correspondence between the quantum and the semiclassical case is damaged to the point that the increase of entropy and quantum uncertainty for regular motion exceeds that for the chaotic case. We demonstrate by direct calculation that this conclusion is the result of mistakenly identifying a regular evolution of the spin-boson system as being chaotic.