Solitons of the constrained Schr\"odinger equations

Abstract

We consider the linear vector Schr\"odinger equation subjected to quadratic constraints. We demonstrate that the resulting nonlinear system is closely related to the Ablowitz-Ladik hierarchy and use this fact to derive the N-soliton solutions for the discussed model. As an example of application of these results we present solitons of some vector nonlinear Schr\"odinger equation with gradient nonlinearity.