Probing Sound Speed of an Optically-Trapped Bose Gas with Periodically Modulated Interactions by Bragg Spectroscopy

Abstract

A Bose-Einstein condensate (BEC) with periodically modulated interactions (PMI) has emerged as a novel kind of periodic superfluid, which has been recently experimentally created using optical Feshbach resonance. In this paper, we are motivated to investigate the superfluidity of a BEC with PMI trapped in an optical lattice (OL). In particular, we explore the effects of PMI on the sound speed and the dynamical structure factor of the model system. Our numerical results, combined with the analytical results in both the weak-potential limit and the tight-binding limit, have shown that the PMI can strongly modify the sound speed of a BEC. Moreover, we have shown that the effects of PMI on sound speed can be experimentally probed via the dynamic structure factor, where the excitation strength toward the first Bogoliubov band exhibits marked difference from the non-PMI one. Our predictions of the effects of PMI on the sound speed can be tested using the Bragg spectroscopy.

Probing the flat band of optically trapped spin-orbital-coupled Bose gases using Bragg spectroscopy

“…[29][30][31]). The presence of flat band is manifest to the eye (see Fig.2 (b1), (c1) and (d1)), as compared to an ordinary band (see Fig.2 (a1)).…”

“…From the dynamic structure factor, the excitation spectrum can then be extracted [30,31,33]. Let us calculate the excitation spectrum and the dynamic structure factor S(q, ω) of the model system for various band structures, from an ordinary band to a perfect flat band.…”

“…In this work, in order to avoid dynamical instability, which is relevant to our detailed calculations, we have limited ourselves to the stable parameter regime [9]. Then the dynamic structure factor can be found via [30,34] …”

“…In particular, the static structure factor for the model system can be immediately read off as [30,34] …”

Unusual behavior of sound velocity of a Bose gas in an optical superlattice at quasi-one-dimension

“…The speed of sound of a BEC in an OL may be measured with a similar technique as was used in references [9,63]. Another option is to employ Bragg spectroscopy [10,11,64] to the excitation spectrum. The sound velocity can be extracted from the slope of the linear part of the excitation spectrum.…”