Matrix isolated barium monofluoride: Assembling a sample of BaF molecules for a measurement of the electron electric dipole moment

TL;DR

This paper reports the creation of a BaF-doped cryogenic solid suitable for electron EDM measurements, achieving a high density of addressable molecules within a small volume for improved experimental sensitivity.

Contribution

It demonstrates a method to produce a dense, solid matrix of BaF molecules with high addressability, enabling continuous access for electron EDM experiments.

Findings

Achieved ~10^10 BaF molecules per mm^3 in the solid.

Molecules are thermalized and accessible for measurement.

The number of molecules matches the target for eEDM experiments.

Abstract

A cryogenic neon solid doped with barium monofluoride (BaF) is created on a cryogenic substrate using a stream of Ne gas and a high-intensity beam of BaF molecules produced in a cryogenic helium-buffer-gas laser-ablation source. The apparatus is designed for eventual use in a measurement of the electron electric dipole moment (eEDM). Laser-induced fluorescence is observed from transitions up to the $B\,^2\Sigma_{1/2}$ state. The number of BaF molecules found to be present in the solid and addressable with this laser transition is approximately 10$^{10}$ per mm$^3$, which is of the same order as the total number of BaF molecules that impact the substrate during the hour of growth time for the solid. As a result, an eventual eEDM measurement could have continual access to an accumulation of an hour's worth of molecules (all of which are contained within a 1-mm$^3$ volume and are thermalized into the ground state), compared to beam experiments which study the molecules from a single ablation during the millisecond-timescale of their passage through a much larger-scale measurement apparatus. The number of BaF molecules observed in the doped solid matches the target value for our planned eEDM measurement.