Quantum Phase Transition with a Simple Variational Ansatz

TL;DR

This paper introduces a simple variational wavefunction to model the quantum phase transition in helium-4, capturing spontaneous symmetry breaking and solidification at 22 atm.

Contribution

It presents a fully explicit, exchange-symmetric variational wavefunction that effectively describes both the phase transition and ground state of a Bose solid.

Findings

Wavefunction undergoes spontaneous symmetry breaking during solidification.

Accurately describes first-order quantum phase transition in helium-4.

Wavefunction is a promising candidate for modeling Bose solids.

Abstract

We study the zero-temperature quantum phase transition between liquid and hcp solid helium-4. We use the variational method with a simple yet exchange-symmetric and fully explicit wavefunction. It is found that the optimized wavefunction undergoes spontaneous symmetry breaking and describes the quantum solidification of helium at 22 atm. The explicit form of the wavefunction allows to consider various contributions to the phase transition. We find that the employed wavefunction is an excellent candidate for describing both a first-order quantum phase transition and the ground state of a Bose solid.