## Matrix elements for the quantum cat map: fluctuations in short windows.(English)Zbl 1187.81131

Summary: We study fluctuations of the matrix coefficients for the quantized cat map. We consider the sum of matrix coefficients corresponding to eigenstates whose eigenphases lie in a randomly chosen window, assuming that the length of the window shrinks with Planck’s constant. We show that if the length of the window is smaller than the square root of Planck’s constant, but larger than the separation between distinct eigenphases, then the variance of this sum is proportional to the length of the window, with a proportionality constant which coincides with the variance of the individual matrix elements corresponding to Hecke eigenfunctions.

### MSC:

 81Q50 Quantum chaos 11L40 Estimates on character sums 11M36 Selberg zeta functions and regularized determinants; applications to spectral theory, Dirichlet series, Eisenstein series, etc. (explicit formulas) 37D20 Uniformly hyperbolic systems (expanding, Anosov, Axiom A, etc.) 37N20 Dynamical systems in other branches of physics (quantum mechanics, general relativity, laser physics)
Full Text: