# Stability analysis of ground states in a one-dimensional trapped spin-1 Bose gas

## TL;DR

This paper investigates the stability of ground states in a one-dimensional trapped spin-1 Bose gas, using advanced numerical methods to analyze how trapping potentials influence stability and dynamical instabilities.

## Contribution

It extends the continuous-time Nesterov method to multi-component systems and applies it to analyze ground state stability in a trapped spin-1 Bose gas.

## Key findings

- Trapping potential preserves the overall stability diagram structure.
- Peak density determines dynamical instability characteristics.
- Homogeneous Bogoliubov predictions match trapped system growth rates when using peak density.

## Abstract

In this work we study the stability properties of the ground states of a spin-1 Bose gas in presence of a trapping potential in one spatial dimension. To set the stage we first map out the phase diagram for the trapped system by making use of a, so-called, continuous-time Nesterov method. We present an extension of the method, which has been previously applied to one-component systems, to our multi-component system. We show that it is a powerful and robust tool for finding the ground states of a physical system without the need of an accurate initial guess. We subsequently solve numerically the Bogoliubov de-Gennes equations in order to analyze the stability of the ground states of the trapped spin-1 system. We find that the trapping potential retains the overall structure of the stability diagram, while affecting the spectral details of each of the possible ground state waveforms. It is also found that the peak density of the trapped system is the characteristic quantity describing dynamical instabilities in the system. Therefore replacing the homogeneous density with the peak density of the trapped system leads to good agreement of the homogeneous Bogoliubov predictions with the numerically observed maximal growth rates of dynamically unstable modes. The stability conclusions in the one-dimensional trapped system are independent of the spin coupling strength and the normalized trap strength over several orders of magnitude of their variation.