Abstract
We present in this paper a uniform technique for the study of differential and difference equations in the Hardy‐Lebesgue space, i.e., the Hilbert space consisting of analytic functions in the unit disk, taking the Schrödinger equation as an example. The approach followed is based on the representation of the Hardy‐Lebesgue space by means of the unilateral shift operator, and reduces the problem of solving the Schrödinger equation to a perturbation problem of non‐self‐adjoint operators in an abstract separable Hilbert space.