Ultracold bosons in lattices with binary disorder

TL;DR

This paper explores the phase diagram of ultracold bosons in lattices with binary disorder, revealing the persistence of the Mott-insulator phase and characterizing the Bose glass phase's properties.

Contribution

It provides a comprehensive analysis of the phase diagram using multiple methods, highlighting the unique effects of binary disorder on quantum phases.

Findings

Mott-insulator phase exists for all disorder strengths

Bose glass compressibility varies widely and can be very low

Finite temperature effects are discussed

Abstract

Quantum phases of ultracold bosons with repulsive interactions in lattices in the presence of quenched disorder are investigated. The disorder is assumed to be caused by the interaction of the bosons with impurity atoms having a large effective mass. The system is described by the Bose-Hubbard Hamiltonian with random on-site energies which have a discrete binary probability distribution. The phase diagram at zero temperature is calculated using several methods like a strong-coupling expansion, an exact numerical diagonalization, and a Bose-Fermi mapping valid in the hard-core limit. It is shown that the Mott-insulator phase exists for any strength of disorder in contrast to the case of continuous probability distribution. We find that the compressibility of the Bose glass phase varies in a wide range and can be extremely low. Furthermore, we evaluate experimentally accessible quantities like the momentum distribution, the static and dynamic structure factors, and the density of excited states. The influence of finite temperature is discussed as well.