A Study of Phase-Space Dynamics for Orthogonal Polynomial Self-Interactions

The phase space dynamics generated by different orthogonal polynomial self-interactions exhibited in higher order nonlinear Schrödinger equation (NLSE) are often less intuitive than those of cubic and quintic nonlinearities. Even for nonlinearities as simple as a cubic in NLSE, the dynamics for generic initial states shows surprising features. In this paper, for the first time, we identify the higher-order nonlinearities in terms of orthogonal polynomials in the generalized NLSE/GPE. More pertinently, we explicate different exotic phase space structures for three specific examples: (i) Hermite, (ii) Chebyshev, and (iii) Laguerre polynomial self-interactions. For the first two self-interactions, we exhibit that the alternating signs of the various higher-order nonlinearities are naturally embedded in these orthogonal polynomials that confirm to the experimental conditions. To simulate the phase-space dynamics that bring about by the Laguerre self-interactions, a source term should necessarily be included in the modified NLSE/GPE. Recent experiments suggest that this modified GPE captures the dynamics of self-bound quantum droplets, in the presence of external source.