Exotic Phase Space Dynamics Generated by Orthogonal Polynomial Self-interactions

TL;DR

This paper explores complex phase space behaviors in a generalized nonlinear Schrödinger equation with orthogonal polynomial self-interactions, revealing exotic structures and linking them to experimental quantum droplet dynamics.

Contribution

It introduces a novel framework expressing higher-order nonlinearities via orthogonal polynomials in the NLSE/GPE, and demonstrates exotic phase space structures for Hermite, Chebyshev, and Laguerre cases.

Findings

Orthogonal polynomial self-interactions produce unique phase space structures.

Alternating signs of nonlinearities are naturally embedded in Hermite and Chebyshev polynomials.

Laguerre self-interactions require a source term, modeling quantum droplets with external sources.

Abstract

The phase space dynamics generated by different orthogonal polynomial self-interactions exhibited in higher order nonlinear Schr\"{o}dinger equation (NLSE) are often less intuitive than those ofcubic and quintic nonlinearities. Even for nonlinearities as simple as a cubic in NLSE, the dynamics for generic initial states shows surprising features. In this Letter, 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 {\it 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.