Abstract
The best upper limit for the electron electric dipole moment was recently set by the ACME collaboration. This experiment measures an electron spin-precession in a cold beam of ThO molecules in their metastable state. Improvement in the statistical and systematic uncertainties is possible with more efficient use of molecules from the source and better magnetometry in the experiment, respectively. Here, we report measurements of several relevant properties of the long-lived state of ThO, and show that this state is a very useful resource for both these purposes. The Q state lifetime is long enough that its decay during the time of flight in the ACME beam experiment is negligible. The large electric dipole moment measured for the Q state, giving rise to a large linear Stark shift, is ideal for an electrostatic lens that increases the fraction of molecules detected downstream. The measured magnetic moment of the Q state is also large enough to be used as a sensitive co-magnetometer in ACME. Finally, we show that the Q state has a large transition dipole moment to the state, which allows for efficient population transfer between the ground state and the Q state via Stimulated Raman Adiabatic Passage (STIRAP). We demonstrate 90 % STIRAP transfer efficiency. In the course of these measurements, we also determine the magnetic moment of C state, the transition dipole moment, and branching ratios of decays from the C state.
Highlights
The best upper limit for the electron electric dipole moment (EDM), de, was recently set by the ACME collaboration: |de| < 1.1 × 10−29 e·cm [1]
The ACME experiment is based on measurement of an electron spin precession in thorium monoxide (ThO) molecules
These molecules are prepared in electron spin superposition states in the metastable H (3∆1) level, where the interaction of an electron EDM is greatly amplified by the effective intra-molecular electric field [6, 7] Eeff ≈ 78 GV/cm
Summary
The best upper limit for the electron electric dipole moment (EDM), de, was recently set by the ACME collaboration: |de| < 1.1 × 10−29 e·cm [1]. We measure a strong transition dipole moment for Q → C which allows for the demonstration of 90% STIRAP efficiency between X ↔ Q via the intermediate C state, with near-saturation of the population transfer over a broad Doppler distribution and spatial extent of the ThO beam. This paves the way for applying the Q state both in a molecular lens and for co-magnetometry in the ACME experiment
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