Elusive structure of helium trimers

TL;DR

This study uses diffusion Monte Carlo simulations to evaluate and rank various helium-helium interaction potentials by comparing their predicted structural properties of helium trimers with recent experimental data, revealing all models predict helium trimers as quantum halo states.

Contribution

The paper introduces a systematic comparison of multiple helium interaction potentials against experimental data using diffusion Monte Carlo, providing a ranking and evaluation of their accuracy.

Findings

All models predict helium trimers as quantum halo states.

The study ranks interaction potentials based on their agreement with experimental correlation functions.

Diffusion Monte Carlo yields exact ground state properties within statistical noise.

Abstract

Over the years many He-He interaction potentials have been developed, some very sophisticated, including various corrections beyond Born-Oppenheimer approximation. Most of them were used to predict properties of helium dimers and trimers, examples of exotic quantum states, whose experimental study proved to be very challenging. Recently, detailed structural properties of helium trimers were measured for the first time, allowing a comparison with theoretical predictions and possibly enabling the evaluation of different interaction potentials. The comparisons already made included adjusting the maxima of both theoretical and experimental correlation functions to one, so the overall agreement between theory and experiment appeared satisfactory. However, no attempt was made to evaluate the quality of the interaction potentials used in the calculations. In this work, we calculate the experimentally measured correlation functions using both new and old potentials, compare them with experimental data and rank the potentials. We use diffusion Monte Carlo simulations at $T=0\ \mathrm{K}$, which give within statistical noise exact results of the ground state properties. All models predict both trimers $^4\mathrm{He}_{3}$ and $^4\mathrm{He}_2{}^3\mathrm{He}$ to be in a quantum halo state.