 
Summary: 853
Tutorial/Article didactique
Angular momenta dynamics
in magnetic and electric field:
Classical and quantum approach
Marcis Auzinsh
Abstract: A standard description of the angular momentum in atomic or molecular physics
is based on quantum mechanics. However, especially at large angularmomentum limit in
molecules, sometimes a classical approach greatly simplifies problems that are extremely
complicated from a quantummechanical viewpoint. The aim of this paper is to examine
the relationship between the classical and quantum descriptions of the angularmomentum
distribution in an ensemble of particles. At first glance, quantum and classical approaches
appear to be absolutely different and have very little in common. In this paper this
relationship is analyzed. It is shown that similarities can be found between the precession of
angular momentum in the external field and the influence of this field upon the wavefunction
phase of a microparticle. The importance of wave function phases is stressed even for
stationary conditions, and some examples of coherent superposition of quantum states are
presented. The general method of how to pass from the quantum approach to a classical one
is formulated. Results are visualized in the form of 3D distribution functions. This approach
allows a graphical interpretation and thus results in a better understanding, sometimes at first
