Collective spin modes of a trapped quantum ferrofluid

TL;DR

This paper reports the experimental observation of a universal collective spin mode in a trapped quantum ferrofluid, demonstrating a sinusoidal oscillation of local spins in a spinor Bose-Einstein condensate that aligns with hydrodynamic predictions.

Contribution

It presents the first observation of a universal collective spin mode in a spinor BEC, independent of atomic spin and contact interactions.

Findings

Spin mode frequency matches zero-point kinetic energy predictions

Oscillation amplitude varies linearly with spatial coordinates

Observations agree with hydrodynamic equations

Abstract

We report on the observation of a collective spin mode in a spinor Bose-Einstein condensate. Initially, all spins point perpendicular to the external magnetic field. The lowest energy mode consists in a sinusoidal oscillation of the local spin around its original axis, with an oscillation amplitude that linearly depends on the spatial coordinates. The frequency of the oscillation is set by the zero-point kinetic energy of the BEC. The observations are in excellent agreement with hydrodynamic equations. The observed spin mode has a universal character, independent of the atomic spin and spin-dependent contact interactions.