Observation of Massless and Massive Collective Excitations with Faraday Patterns in a Two-Component Superfluid

TL;DR

This paper experimentally measures the dispersion relations of density and spin excitations in a two-component superfluid, revealing how coherent coupling induces a finite mass in spin modes through Faraday wave patterns.

Contribution

It introduces a novel parametric spectroscopic method using transverse confinement modulation to study collective excitations in ultracold superfluids, demonstrating mass acquisition in spin modes.

Findings

Density and spin modes' dispersion relations measured.

Coherent coupling reduces phase symmetry.

Spin modes acquire finite mass due to coupling.

Abstract

We report on the experimental measurement of the dispersion relation of the density and spin collective excitation modes in an elongated two-component superfluid of ultracold bosonic atoms. Our parametric spectroscopic technique is based on the external modulation of the transverse confinement frequency, leading to the formation of density and spin Faraday waves. We show that the application of a coherent coupling between the two components reduces the phase symmetry and gives a finite mass to the spin modes.