Semiclassical measures and the Schrödinger flow on Riemannian manifolds

In this article we study limits of Wigner distributions (the so-called semiclassical measures) corresponding to sequences of solutions to the free Schrödinger equation on a Riemannian manifold (or equivalently, to sequences of solutions to the semiclassical Schrödinger equation at times of the order of 1/h, the inverse of the semiclassical parameter h). Some general results are presented, among which a weak version of Egorov’s theorem that holds in this setting. A complete characterization is given for the Euclidean space and Zoll manifolds (that is, manifolds with periodic geodesic flow) via averaging formulae relating the semiclassical measures corresponding to the evolution to those of the initial states. The case of the flat torus is also addressed; it is shown that non-classical behavior may occur when energy concentrates on resonant frequencies. Moreover, we present an example showing that the semiclassical measures associated to a sequence of states no loger determines those of their evolutions. Finally, some results concerning the equation with a potential are presented. Mathematics Subject Classification: Primary 81Q20; Secondary 37J35, 37N20, 58J47.