Roton-Maxon Excitation Spectrum of Bose Condensates in a Shaken Optical Lattice

TL;DR

This paper experimentally demonstrates a roton-maxon excitation spectrum in a Bose condensate within a shaken optical lattice, revealing controllable superfluid features similar to those in helium.

Contribution

It provides the first experimental observation of a roton-maxon spectrum in a shaken optical lattice and links it to the lattice's double-well dispersion and controllable parameters.

Findings

Observation of roton-maxon spectrum in Bose condensates

Control of spectrum via lattice shaking and interactions

Agreement with a modified-Bogoliubov theoretical model

Abstract

We present experimental evidence showing that an interacting Bose condensate in a shaken optical lattice develops a roton-maxon excitation spectrum, a feature normally associated with superfluid helium. The roton-maxon feature originates from the double-well dispersion in the shaken lattice, and can be controlled by both the atomic interaction and the lattice shaking amplitude. We determine the excitation spectrum using Bragg spectroscopy and measure the critical velocity by dragging a weak speckle potential through the condensate - both techniques are based on a digital micromirror device. Our dispersion measurements are in good agreement with a modified-Bogoliubov model.