Collision-induced three-body polarizability of helium

TL;DR

This paper presents first-principles calculations of helium's three-body polarizability and dielectric virial coefficient, improving accuracy for optical pressure standards and quantum thermal metrology.

Contribution

It introduces an ab initio method for determining helium's three-body polarizability and virial coefficient, with uncertainty quantification and analytic models, advancing precision in quantum thermometry.

Findings

Significant discrepancy with experimental data above 200 K.

Developed analytic functions for polarizability and uncertainty.

Provided improved theoretical data for optical pressure standards.

Abstract

We present first-principles theoretical determination of the three-body polarizability and the third dielectric virial coefficient of helium. Coupled-cluster theory and the full configuration interaction procedure were used to perform required electronic structure calculations. The mean absolute relative uncertainty of the trace of the three-body polarizability tensor, resulting from the incompleteness of orbital basis set, was determined using extrapolation techniques. Additional uncertainty due to approximate treatment of triple and the neglect of higher excitations was estimated using full configuration interaction calculations. An analytic function was developed to describe the behavior of the polarizability and its asymptotic decay to three-atomic and atom-diatom fragmentation channels. We also developed an analytic function describing the local behavior of the total uncertainty of our calculations. Using both fits we calculated the third dielectric virial coefficient and its uncertainty using the classical and semiclassical Feynman-Hibbs approaches. The results of our calculations were compared with available experimental data and with recent Path-Integral Monte Carlo (PIMC) calculations employing the so-called superposition approximation of the three-body polarizability. For temperatures above 200 K we observed significant discrepancy between the classical results obtained using either the superposition approximation or the ab initio computed polarizability. The theoretical data reported in this work eliminate the main accuracy bottleneck of the development of optical pressure standard and are expected to facilitate further progress in the field of quantum thermal metrology