Multi-component gap solitons in spinor Bose-Einstein condensates

TL;DR

This paper models the nonlinear behavior of spinor Bose-Einstein condensates in optical lattices, revealing the existence of multi-component gap solitons, non-SMA localized states, and controllable spin-mixing dynamics.

Contribution

It introduces the concept of non-SMA multi-component localized states in spinor BECs and explores their unique properties and controllability.

Findings

Existence of vector gap solitons and self-trapped waves within band gaps.

Identification of non-SMA states with Josephson-like oscillations and self-magnetization.

Demonstration of controlled spin-mixing dynamics via external magnetic fields.

Abstract

We model the nonlinear behaviour of spin-1 Bose-Einstein condensates (BECs) with repulsive spin-independent interactions and either ferromagnetic or anti-ferromagnetic (polar) spin-dependent interactions, loaded into a one-dimensional optical lattice potential. We show that both types of BECs exhibit dynamical instabilities and may form spatially localized multi-component structures. The localized states of the spinor matter waves take the form of vector gap solitons and self-trapped waves that exist only within gaps of the linear Bloch-wave band-gap spectrum. Of special interest are the nonlinear localized states that do not exhibit a common spatial density profile shared by all condensate components, and consequently cannot be described by the single mode approximation (SMA), frequently employed within the framework of the mean-field treatment. We show that the non-SMA states can exhibits Josephson-like internal oscillations and self-magnetisation, i.e. intrinsic precession of the local spin. Finally, we demonstrate that non-stationary states of a spinor BEC in a lattice exhibit coherent undamped spin-mixing dynamics, and that their controlled conversion into a stationary state can be achieved by the application of an external magnetic field.