Thermal Correction to the Molar Polarizability of a Boltzmann Gas

TL;DR

This paper calculates the thermal relativistic correction to the molar polarizability of atomic gases, which is relevant for high-precision measurements and SI unit redefinition efforts.

Contribution

It introduces a new theoretical calculation of the relativistic thermal correction to atomic polarizability, highlighting its significance over blackbody radiation effects.

Findings

Relativistic correction dominates thermal shifts in polarizability.

The correction is small but significant for precision measurements.

Thermal effects are crucial for accurate fundamental constant determinations.

Abstract

Metrology in atomic physics has been crucial for a number of advanced determinations of fundamental constants. In addition to very precise frequency measurements, the molar polarizability of an atomic gas has recently also been measured very accurately. Part of the motivation for the measurements is due to ongoing efforts to redefine the International System of Units (SI) for which an accurate value of the Boltzmann constant is needed. Here, we calculate the dominant shift of the molar polarizability in an atomic gas due to thermal effects. It is given by the relativistic correction to the dipole interaction, which emerges when the probing electric field is Lorenz transformed into the rest frame of the atoms that undergo thermal motion. While this effect is small when compared to currently available experimental accuracy, the relativistic correction to the dipole interaction is much larger than the thermal shift of the polarizability induced by blackbody radiation.