Collective modes and superfluidity of a two-dimensional ultracold Bose gas

TL;DR

This paper investigates the response of a two-dimensional ultracold Bose gas to a moving lattice, revealing how interaction strength influences collective modes, heating, and the hybridization of first and second sound, advancing understanding of superfluidity.

Contribution

It provides a quantitative analysis of collective modes and superfluidity in 2D Bose gases, including the identification of sound mode hybridization and experimental detection methods.

Findings

Heating rate depends on interaction strength and temperature.

First and second sound modes can be identified and hybridize.

Proposes experimental detection of sound mode hybridization.

Abstract

The collective modes of a quantum liquid shape and impact its properties profoundly, including its emergent phenomena such as superfluidity. Here we present how a two-dimensional Bose gas responds to a moving lattice potential. In particular we discuss how the induced heating rate depends on the interaction strength and the temperature. This study is motivated by the recent measurements of Sobirey {\it et al.} arXiv:2005.07607 (2020), for which we provide a quantitative understanding. Going beyond the existing measurements, we demonstrate that this probing method allows to identify first and second sound in quantum liquids. We show that the two sound modes undergo hybridization as a function of interaction strength, which we propose to detect experimentally. This gives a novel insight into the two regimes of Bose gases, defined via the hierarchy of sounds modes.