Onset of a modulational instability in trapped dipolar Bose-Einstein condensates

TL;DR

This paper investigates the phase transitions of trapped dipolar Bose-Einstein condensates, identifying conditions for adiabatic transformation or modulational instability leading to multiple droplets, thus clarifying the phase diagram of such systems.

Contribution

It provides the first detailed analysis of the onset of modulational instability in finite-sized dipolar BECs, connecting different regimes and identifying a critical trap aspect ratio.

Findings

Critical aspect ratio for instability: 1.87(14)

Observation of adiabatic BEC to droplet transformation

Identification of a multistable region with multiple droplets

Abstract

We explore the phase diagram of a finite-sized dysprosium dipolar Bose-Einstein condensate in a cylindrical harmonic trap. We monitor the final state after the scattering length is lowered from the repulsive BEC regime to the quantum droplet regime. Either an adiabatic transformation between a BEC and a quantum droplet is obtained or, above a critical trap aspect ratio $\lambda_{\rm c}=1.87(14)$, a modulational instability results in the formation of multiple droplets. This is in full agreement with the predicted structure of the phase diagram with a crossover region below $\lambda_{\rm c}$ and a multistable region above. Our results provide the missing piece connecting the previously explored regimes resulting in a single or multiple dipolar quantum droplets.