Quantum Phase Diagram of Bosons in Optical Lattices

TL;DR

This paper develops two analytical methods to accurately determine the quantum phase boundary between Mott insulator and superfluid phases in bosonic optical lattices, aligning well with numerical simulations.

Contribution

It introduces a variational and an effective potential approach to improve upon mean-field results for the MI-SF transition in optical lattices.

Findings

Enhanced accuracy of phase boundary predictions

Agreement with Quantum Monte-Carlo simulations

Applicable to arbitrary lattice dimensions

Abstract

We work out two different analytical methods for calculating the boundary of the Mott-insulator-superfluid (MI-SF) quantum phase transition for scalar bosons in cubic optical lattices of arbitrary dimension at zero temperature which improve upon the seminal mean-field result. The first one is a variational method, which is inspired by variational perturbation theory, whereas the second one is based on the field-theoretic concept of effective potential. Within both analytical approaches we achieve a considerable improvement of the location of the MI-SF quantum phase transition for the first Mott lobe in excellent agreement with recent numerical results from Quantum Monte-Carlo simulations in two and three dimensions. Thus, our analytical results for the whole quantum phase diagram can be regarded as being essentially exact for all practical purposes.