Phase Diagram of Bosonic Atoms in Two-Color Superlattices

TL;DR

This paper maps out the phase diagram of bosonic atoms in one- and two-color superlattices, revealing new phases like localized and quasi Bose-glass states, and clarifies the relationship between physical quantities and phase transitions.

Contribution

It introduces a detailed analysis of the phase diagram of bosons in superlattices, including the identification of new phases and the relationship between superfluid fraction and interference patterns.

Findings

Identification of localized and quasi Bose-glass phases.

Superfluid fraction cannot be directly probed by interference patterns.

Exact numerical solutions support the phase diagram mapping.

Abstract

We investigate the zero temperature phase diagram of a gas of bosonic atoms in one- and two-color standing-wave lattices in the framework of the Bose-Hubbard model. We first introduce some relevant physical quantities; superfluid fraction, condensate fraction, quasimomentum distribution, and matter-wave interference pattern. We then discuss the relationships between them on the formal level and show that the superfluid fraction, which is the relevant order parameter for the superfluid to Mott-insulator transition, cannot be probed directly via the matter wave interference patterns. The formal considerations are supported by exact numerical solutions of the Bose-Hubbard model for uniform one-dimensional systems. We then map out the phase diagram of bosons in non-uniform lattices. The emphasis is on optical two-color superlattices which exhibit a sinusoidal modulation of the well depth and can be easily realized experimentally. From the study of the superfluid fraction, the energy gap, and other quantities we identify new zero-temperature phases, including a localized and a quasi Bose-glass phase, and discuss prospects for their experimental observation.