Conservation laws for the nonlinear Schrödinger equation (Q1071181)

The purpose of the paper is to obtain a method which allows to derive conservation laws of the quantum nonlinear Schrödinger equation \(i \psi_ t=-\psi_{xx}+2c \psi^{\dag}\psi^ 2\) where \(\psi\) is interpreted as a two dimensional quantum field. The heart of the method is the construction of an operator P which intertwines the Laplacian with boundary conditions corresponding to the Hamiltonian \((\partial /\partial x_{k+1}-\partial /\partial x_ k)F=cF,\) \(c>0\) with the Laplacian with Neumann boundary conditions \((\partial /\partial x_{k+1}-\partial /\partial x_ k)F=0.\) Of the infinitely many conservation laws the first four are derived explicitly. The fourth one shows a difference to the analogous classical one. The three first conservation laws reproduce an earlier result by \textit{H. B. Thacker} [Phys. Rev. D 17, 1031 (1978)].