Non-perturbative solution of nonlinear Heisenberg equations

A new non-perturbative method of solution of the nonlinear Heisenberg equat ions in a finite-dimensional subspace is illustrated. The method, being a c ounterpart of the traditional Schrodinger picture method, is based on a fin ite operator expansion into the elementary processes. It provides us with i nsight into the nonlinear quantal interaction from a different point of vie w. Thus, one can investigate the nonlinear system in both pictures of quant um mechanics.