On quantum ergodicity for linear maps of the torus

We prove a strong version of quantum ergodicity for linear hyperbolic maps of the torus (''cat maps''). We show that there is a density one sequence of integers so that as N tends to infinity along this sequence, all eigenfunctions of the quantum propagator at inverse Planck constant N are uniformly distributed.A key step in the argument is to show that for a hyperbolic matrix in the modular group, there is a density one sequence of integers N for which its order (or period) modulo N is somewhat larger than √(N). (orig.)