STIRAP preparation of a coherent superposition of ThO $H^3\Delta_1$ states for an improved electron EDM measurement

TL;DR

This paper introduces an improved STIRAP-based method for preparing ThO molecules in a superposition state, enhancing the sensitivity of electron EDM measurements by increasing transfer efficiency.

Contribution

It presents a novel application of STIRAP to efficiently prepare ThO $H^3 riangle_1$ states for electron EDM experiments, achieving 75% transfer efficiency.

Findings

Achieved 75% transfer efficiency in state preparation.

Demonstrated feasibility of STIRAP in complex molecular systems.

Enhanced potential for next-generation electron EDM measurements.

Abstract

Experimental searches for the electron electric dipole moment (EDM) probe new physics beyond the Standard Model. The current best EDM limit was set by the ACME Collaboration [Science \textbf{343}, 269 (2014)], constraining time reversal symmetry ($T$) violating physics at the TeV energy scale. ACME used optical pumping to prepare a coherent superposition of ThO $H^3\Delta_1$ states that have aligned electron spins. Spin precession due to the molecule's internal electric field was measured to extract the EDM. We report here on an improved method for preparing this spin-aligned state of the electron by using STIRAP. We demonstrate a transfer efficiency of $75\pm5\%$, representing a significant gain in signal for a next generation EDM experiment. We discuss the particularities of implementing STIRAP in systems such as ours, where molecular ensembles with large phase-space distributions are transfered via weak molecular transitions with limited laser power and limited optical access.