Strong dipolar effects in a quantum ferrofluid

TL;DR

This paper demonstrates the creation of a Chromium Bose-Einstein condensate with dominant dipolar interactions, revealing unique anisotropic effects and suppression of typical BEC expansion signatures, advancing the study of quantum ferrofluids.

Contribution

It introduces a method to enhance dipolar interactions in a BEC using Feshbach resonance, enabling exploration of quantum ferrofluid properties.

Findings

Dipolar interactions become comparable to contact interactions in the BEC.

The aspect ratio of the condensate changes due to dipolar effects.

Strong dipolar interactions can suppress the typical inversion of ellipticity during expansion.

Abstract

We report on the realization of a Chromium Bose-Einstein condensate (BEC) with strong dipolar interaction. By using a Feshbach resonance, we reduce the usual isotropic contact interaction, such that the anisotropic magnetic dipole-dipole interaction between 52Cr atoms becomes comparable in strength. This induces a change of the aspect ratio of the cloud, and, for strong dipolar interaction, the inversion of ellipticity during expansion - the usual "smoking gun" evidence for BEC - can even be suppressed. These effects are accounted for by taking into account the dipolar interaction in the superfluid hydrodynamic equations governing the dynamics of the gas, in the same way as classical ferrofluids can be described by including dipolar terms in the classical hydrodynamic equations. Our results are a first step in the exploration of the unique properties of quantum ferrofluids.