Probing QED and fundamental constants through laser spectroscopy of vibrational transitions in HD+

TL;DR

This study uses laser spectroscopy of HD+ to test quantum electrodynamics and measure fundamental constants with unprecedented precision, confirming theoretical predictions and enabling new physics constraints.

Contribution

It provides the most precise comparison between theory and experiment for molecular hydrogen ions, validating high-order QED and enabling measurement of fundamental constants.

Findings

The experimental and theoretical frequencies agree within 0.6(1.1) ppb.

Confirmed the validity of high-order QED in molecules.

Enabled constraints on fifth forces and higher-dimensional theories.

Abstract

The simplest molecules in nature, molecular hydrogen ions in the form of H2+ and HD+, provide an important benchmark system for tests of quantum electrodynamics in complex forms of matter. Here, we report on such a test based on a frequency measurement of a vibrational overtone transition in HD+ by laser spectroscopy. We find that the theoretical and experimental frequencies are equal to within 0.6(1.1) parts per billion, which represents the most stringent test of molecular theory so far. Our measurement not only confirms the validity of high-order quantum electrodynamics in molecules, but also enables the long predicted determination of the proton-to-electron mass ratio from a molecular system, as well as improved constraints on hypothetical fifth forces and compactified higher dimensions at the molecular scale. With the perspective of comparisons between theory and experiment at the 0.01 part-per-billion level, our work demonstrates the potential of molecular hydrogen ions as a probe of fundamental physical constants and laws.