2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/183773We calculate exactly matrix elements between states that are not eigenstates of the quantum XY model for general anisotropy. Such quantities therefore describe non equilibrium properties of the system; the Hamiltonian does not contain any time dependence. These matrix elements are expressed as a sum of Pfaffians. For single particle excitations on the ground state the Pfaffians in the sum simplify to determinants.11 pages, no figures; revtex. Minor changes in the text; list of refs. modifiedStrongly Correlated ElectronsHigh Energy Physics - TheoryMathematical PhysicsExactly Solvable and Integrable Systemstext