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arXiv:1603.07707 · Physical Review A

Stimulated Raman adiabatic passage preparation of a coherent superposition of ThO H3Δ1 states for an improved electron electric-dipole-moment measurement

Cristian Daniel Panda, Brendon O'Leary, Adam West, Jacob Baron, Paul Hess, C. Hoffman, Emil Kirilov, Chris Overstreet, Elizabeth P. West, David P. DeMille, John M. Doyle, G. Gabrielse

Published May 16, 2016• 32 citations
arXivHTMLPDF

Abstract

A quantum-state preparation scheme is demonstrated for the next generation ACME experiment searching for the electron electric dipole moment in ThO molecules, where the stimulated Raman adiabatic passage technique, together with other experimental improvements, brings in at least a 75 times increase in combined preparation and detection efficiency of the molecules in the target state.

DOI
10.1103/physreva.93.052110

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A quantum-state preparation scheme is demonstrated for the next generation ACME experiment searching for the electron electric dipole moment in ThO molecules, where the stimulated Raman adiabatic passage technique, together with other experimental improvements, brings in at least a 75 times increase in combined preparation and detection efficiency of the molecules in the target state.
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Abstract The electric dipole moment of the electron (eEDM) can be measured with high precision using heavy polar molecules. In this paper, we report on a series of new techniques that have improved the statistical sensitivity of the YbF eEDM experiment. We increase the number of molecules participating in the experiment by an order of magnitude using a carefully designed optical pumping scheme. We also increase the detection efficiency of these molecules by another order of magnitude using an optical cycling scheme. In addition, we show how to destabilise dark states and reduce backgrounds that otherwise limit the efficiency of these techniques. Together, these improvements allow us to demonstrate a statistical sensitivity of 1.8 × 10−28 e cm after one day of measurement, which is 1.2 times the shot-noise limit. The techniques presented here are applicable to other high-precision measurements using molecules.
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Abstract The current best upper limit for electron electric dipole moment (EDM), |d e| < 1.1 × 10−29 e cm (90% confidence), was set by the ACME Collaboration in 2018. The ACME experiment uses a spin-precession measurement in a cold beam of thorium monoxide (ThO) molecules to detect d e. An improvement in statistical uncertainty would be possible with more efficient use of molecules from the cryogenic buffer gas beam source. Here, we demonstrate electrostatic focusing of the ThO beam with a hexapole lens. This results in a factor of 16 enhancement in the molecular flux detectable downstream, in a beamline similar to that built for the next generation of ACME. We also demonstrate an upgraded rotational cooling scheme that increases the ground state population by 3.5 times compared to no cooling, consistent with expectations and a factor of 1.4 larger than previously in ACME. When combined with other demonstrated improvements, we project over an order of magnitude improvement in statistical sensitivity for the next generation ACME electron EDM search.
The rovibrational dynamics of stimulated Raman adiabatic passage (STIRAP) through permanent dipole moment transitions are investigated theoretically using a time-dependent quantum wave packet method for the ground electronic state of an HF molecule. The two basic STIRAP processes, $\ensuremath{\Lambda}$ and ladder systems, are simulated. The calculated results show that nearly 100100%100 of the population can be transferred to the target state. Besides the interested transitions, the pulses can induce other transitions which affect the dynamics of STIRAP. The final populations of the initial and target states depend on delay time.
We describe a spin interferometer using ultracold YbF molecules and develop the complete set of techniques needed to measure the electron's electric dipole moment, ded_ede​, with this apparatus. The molecules are cooled in an optical molasses and prepared in a single internal quantum state. A Raman transition prepares a spin superposition which evolves in parallel magnetic and electric fields before a second Raman transition maps the phase onto the populations of two hyperfine states. These populations are read out using detectors that have spatial and temporal resolution and approach unit efficiency. We characterize the efficiencies and fidelities of all these steps and evaluate the sensitivity of this approach to measuring ded_ede​.