Weakly interacting two-dimensional system of dipoles: limitations of mean-field theory

TL;DR

This paper investigates a 2D dipolar Bose gas, revealing that mean-field theory significantly deviates from diffusion Monte Carlo results in predicting the ground state and collective excitations.

Contribution

It provides a detailed comparison between Monte Carlo simulations and mean-field theory, highlighting the limitations of the latter for 2D dipolar systems.

Findings

Quantitative differences in ground-state energy predictions

Discrepancies in static structure factor and pair distribution function

Altered frequency of the lowest breathing mode in traps

Abstract

We consider a homogeneous 2D Bose gas with repulsive dipole-dipole interactions. The ground-state equation of state, calculated using the Diffusion Monte Carlo method, shows quantitative differences with predictions of commonly used Gross-Pitaevskii mean-field theory. The static structure factor, pair distribution function and condensate fraction are calculated in a wide range of the gas parameter. Differences with mean-field theory are reflected in the frequency of the lowest ``breathing'' mode for harmonically trapped systems.