# Observation of a Modulational Instability in Bose-Einstein condensates

## TL;DR

This paper reports the experimental observation of modulational instability in elongated Bose-Einstein condensates of rubidium-85, linking the breakup into solitons with theoretical predictions from stability analysis of the nonlinear Schrödinger equation.

## Contribution

It demonstrates the first direct experimental observation of modulational instability in Bose-Einstein condensates and confirms theoretical predictions using a one-dimensional effective model.

## Key findings

- The number of observed solitons matches the predictions from the fastest growing sidebands.
- Modulational instability is identified as the key mechanism behind the condensate breakup.
- Experimental data supports the theoretical model based on the nonlinear Schrödinger equation.

## Abstract

We observe the breakup dynamics of an elongated cloud of condensed $^{85}$Rb atoms placed in an optical waveguide. The number of localized spatial components observed in the breakup is compared with the number of solitons predicted by a plane-wave stability analysis of the nonpolynomial nonlinear Schr\"odinger equation, an effective one-dimensional approximation of the Gross-Pitaevskii equation for cigar-shaped condensates. It is shown that the numbers predicted from the fastest growing sidebands are consistent with the experimental data, suggesting that modulational instability is the key underlying physical mechanism driving the breakup.