Matter-wave solitons in radially periodic potentials

TL;DR

This paper explores the existence, stability, and dynamics of matter-wave solitons in a radially periodic potential, revealing new types of nonlinear localized states in Bose-Einstein condensates with potential applications in photonic systems.

Contribution

It introduces the concept of radial gap solitons in 2D BECs with radial optical lattices, a novel class of nonlinear localized states absent in linear regimes.

Findings

Radial gap solitons are found in repulsive BEC models.

Stable annular and ring-shaped localized states are demonstrated.

Collision behaviors include collapse and merging without collapse.

Abstract

We investigate two-dimensional (2D) states of Bose-Einstein condensates (BEC) with self-attraction or self-repulsion, trapped in an axially symmetric optical-lattice potential periodic along the radius. Unlike previously studied 2D models with Bessel lattices, no localized states exist in the linear limit of the present model, hence all localized states are truly nonlinear ones. We consider the states trapped in the central potential well, and in remote circular troughs. In both cases, a new species, in the form of \textit{radial gap solitons}, are found in the repulsive model (the gap soliton trapped in a circular trough may additionally support stable dark-soliton pairs). In remote troughs, stable localized states may assume a ring-like shape, or shrink into strongly localized solitons. The existence of stable annular states, both azimuthally uniform and weakly modulated ones, is corroborated by simulations of the corresponding Gross-Pitaevskii equation. Dynamics of strongly localized solitons circulating in the troughs is also studied. While the solitons with sufficiently small velocities are stable, fast solitons gradually decay, due to the leakage of matter into the adjacent trough under the action of the centrifugal force. Collisions between solitons are investigated too. Head-on collisions of in-phase solitons lead to the collapse; $\pi $-out of phase solitons bounce many times, but eventually merge into a single soliton without collapsing. The proposed setting may also be realized in terms of spatial solitons in photonic-crystal fibers with a radial structure.