Manipulating the Mott lobes: optical lattice bosons coupled to an array of atomic quantum dots

TL;DR

This paper studies how coupling optical lattice bosons to atomic quantum dots alters the Mott insulator to superfluid transition, revealing controllable phase diagram modifications and a novel order parameter linked to pseudospin magnetization.

Contribution

It introduces an assisted tunneling mechanism via atomic quantum dots, analyzing its impact on the Mott lobes and phase transitions in the Bose-Hubbard model.

Findings

Mott-superfluid transition persists but Mott lobes depend on system parameters.

Reversal of the hierarchy of Mott lobes can occur.

Mott lobes can disappear with direct tunneling, leading to a superfluid phase.

Abstract

We analyze quantum phase transitions in a system of optical lattice bosons coupled to an array of atomic quantum dots, or pseudospins-1/2. The system parallels the Bose-Hubbard model with a single difference of the direct tunneling between the lattice sites being replaced by an assisted tunneling via coupling to the atomic quantum dots. We calculate the phase diagram of the combined system, numerically within the Gutzwiller ansatz and analytically using the mean-field decoupling approximation. The result of the assisted Bose-Hubbard model is that the Mott-superfluid transition still takes place, however, the Mott lobes strongly depend on the system parameters such as the detuning. One can even reverse the usual hierarchy of the lobes with the first lobe becoming the smallest. The phase transition in the bosonic subsystem is accompanied by a magnetization rotation in the pseudospin subsystem with the tilting angle being an effective order parameter. When direct tunneling is taken into account, the Mott lobes can be made disappear and the bosonic subsystem becomes superfluid throughout.