Optical pumping and laser slowing of a heavy molecule

TL;DR

This paper demonstrates effective laser slowing of BaF molecules by reducing leakage channels through microwave remixing and optical pumping, enabling future precision eEDM measurements.

Contribution

It introduces a combined microwave and optical pumping technique to minimize leakage in laser slowing of heavy molecules like BaF.

Findings

Leakage fraction reduced to 10^-5

BaF molecules slowed from 80 m/s to near-zero velocity

Establishes foundation for laser-cooled heavy molecule eEDM experiments

Abstract

Precision measurements of the electron's electric dipole moment (eEDM) are critical for testing fundamental symmetries in particle physics, and heavy polar molecules-such as barium monofluoride (BaF)-have emerged as promising candidates for advancing the sensitivity. However, the achievement of a 3D magneto-optical trap (MOT) required slowing BaF molecules to near-zero velocity by scattering over 10^4 photons per molecule, demanding a quasi-cycling transition with minimal leakage. We present a detailed study of the leakage channels, including higher vibrational and rotational states. By combining microwave remixing with optical pumping of rotational and vibrational dark states, we reduced the total leakage fraction to 10^-5. Using frequency-chirped laser slowing, we slowed a subset of buffer-gas-cooled BaF molecules from approximately 80 m/s to near-zero velocity, which is critical for efficient MOT loading. This work establishes the technical foundation for precision eEDM measurements using laser-cooled heavy molecules.