Bragg spectroscopy of clean and disordered lattice bosons in one dimension: a spectral fingerprint of the Bose glass

TL;DR

This paper investigates the dynamic structure factor of one-dimensional lattice bosons using Bragg spectroscopy, revealing spectral signatures of superfluid, Mott, and Bose glass phases, and distinguishing localization mechanisms in disordered systems.

Contribution

It provides a detailed analysis of the dynamic structure factor in clean and disordered 1D Bose gases, identifying spectral fingerprints of the Bose glass phase and localization mechanisms.

Findings

Identification of a gapped doublon mode in the clean regime.

Spectral signatures of localized excitations in disordered systems.

Potential to estimate the superfluid-Bose glass transition point from spectral data.

Abstract

We study the dynamic structure factor of a one-dimensional Bose gas confined in an optical lattice and modeled by the Bose-Hubbard Hamiltonian, using a variety of numerical and analytical approaches. The dynamic structure factor, experimentally measurable by Bragg spectroscopy, is studied in three relevant cases: in the clean regime, featuring either a superfluid or a Mott phase; and in the presence of two types of (quasi-)disordered external potentials: a quasi-periodic potential obtained from a bichromatic superlattice and a random-box disorder - both featuring a Bose glass phase. In the clean case, we show the emergence of a gapped doublon mode (corresponding to a repulsively bound state) for incommensurate filling, well separated from the low-energy acoustic mode. In the disordered case, we show that the dynamic structure factor provides a direct insight into the spatial structure of the excitations, unveiling their localized nature, which represents a fundamental signature of the Bose glass phase. Furthermore, it provides a clear fingerprint of the very nature of the localization mechanism which differs for the two kinds of disorder potentials we consider. In special cases, the dynamic structure factor may provide an estimate of the position of the localization transition from superfluid to Bose glass, in a complementary manner to the information deduced from the momentum distribution.