Ultrahigh-precision measurement of the $n=2$ triplet P fine structure of atomic helium using frequency-offset separated oscillatory fields

TL;DR

This paper reports a highly precise measurement of the helium $n=2$ $^3$P fine structure interval using the novel FOSOF technique, significantly advancing the accuracy of quantum electrodynamics tests.

Contribution

The study introduces the FOSOF method for measuring helium fine structure with unprecedented precision, improving previous measurements and enabling better tests of fundamental physics.

Findings

Measured the $2^3$P$_2 o 2^3$P$_1$ interval as 2,291,176,590(25) Hz

Achieved a major precision improvement over prior measurements

Supports refined tests of quantum electrodynamics and fundamental constants

Abstract

For decades, improved theory and experiment of the $n=2$ $^3$P fine structure of helium have allowed for increasingly-precise tests of quantum electrodynamics, determinations of the fine-structure constant $\alpha$, and limitations on possible beyond-the-Standard-Model physics. Here we use the new frequency-offset separated-oscillatory-fields (FOSOF) technique to measure the $2^3$P$_2\!\!\to\!2^3$P$_1$ interval. Our result of $2\,291\,176\,590(25)$~Hz represents a major step forward in precision for helium fine-structure measurements.