Order by disorder in frustration-free systems: a Quantum Monte Carlo study of a two-dimensional PXP model

TL;DR

This paper investigates a two-dimensional PXP model where quantum fluctuations lift classical degeneracy, leading to long-range order and a thermal phase transition, using large-scale Quantum Monte Carlo simulations.

Contribution

It introduces an order by disorder mechanism in a frustration-free system and demonstrates quantum fluctuation effects via Quantum Monte Carlo methods.

Findings

Quantum fluctuations lift degeneracy and induce charge-density-wave order.

Identifies a thermal phase transition with 2D Ising universality.

Proposes a simple trial wavefunction for the ground state.

Abstract

In this study, an order by disorder mechanism has been proposed in a two-dimensional PXP model, where the extensive degeneracy of the classical ground-state manifold is due to strict occupation constraints instead of geometrical frustrations. By performing an unbias large-scale quantum monte carlos simulation, we find that local quantum fluctuations, which usually work against long-range ordering, lift the macroscopic classical degeneracy and give rise to a compressible ground state with charge-density-wave long-range order. A simple trial wavefunction has been proposed to capture the essence of the ground-state of the two-dimensional PXP model. The finite temperature properties of this model have also been studied, and we find a thermal phase transition with an universality class of two-dimensional Ising model.