Collective Dipole Oscillation of a Spin-Orbit Coupled Bose-Einstein Condensate

TL;DR

This study experimentally investigates the collective dipole oscillation in a spin-orbit coupled Bose-Einstein condensate, revealing anharmonic behaviors, a method to measure spin polarization susceptibility, and observing divergence at a quantum phase transition.

Contribution

It provides the first experimental demonstration of the link between dipole oscillation dynamics and spin polarization susceptibility in spin-orbit coupled BECs, confirming theoretical predictions.

Findings

Observation of amplitude-dependent frequency and finite oscillation frequency at divergent effective mass.

Experimental measurement of spin polarization susceptibility via dipole oscillation.

Detection of divergence in polarization susceptibility at the quantum phase transition.

Abstract

We present an experimental study of the collective dipole oscillation of a spin-orbit coupled Bose-Einstein condensate in a harmonic trap. Dynamics of the center-of-mass dipole oscillation is studied in a broad parameter region, as a function of spin-orbit coupling parameters as well as oscillation amplitude. Anharmonic properties beyond effective-mass approximation are revealed, such as amplitude-dependent frequency and finite oscillation frequency at place with divergent effective mass. These anharmonic behaviors agree quantitatively with variational wave-function calculations. Moreover, we experimentally demonstrate a unique feature of spin-orbit coupled system predicted by a sum-rule approach, stating that spin polarization susceptibility--a static physical quantity--can be measured via dynamics of dipole oscillation. The divergence of polarization susceptibility is observed at the quantum phase transition that separates magnetic nonzero-momentum condensate from nonmagnetic zero-momentum phase. The good agreement between the experimental and theoretical results provides a bench mark for recently developed theoretical approaches.