The metastable Q <sup>3</sup>Δ<sub>2</sub> state of ThO: a new resource for the ACME electron EDM search
X Wu, Z Han, J Chow, D G Ang, C Meisenhelder, C D Panda, E P West, G Gabrielse, J M Doyle, D DeMille
Abstract
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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>H</mml:mi> <mml:mspace width="0.50em"/> <mml:msup> <mml:mrow> <mml:mo stretchy="false">(</mml:mo> </mml:mrow> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> </mml:msup> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">Δ</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>1</mml:mn> </mml:mrow> </mml:msub> <mml:mo stretchy="false">)</mml:mo> </mml:math> 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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>Q</mml:mi> <mml:mspace width="0.50em"/> <mml:msup> <mml:mrow> <mml:mo stretchy="false">(</mml:mo> </mml:mrow> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> </mml:msup> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">Δ</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> <mml:mo stretchy="false">)</mml:mo> </mml:math> 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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>C</mml:mi> <mml:mspace width="0.50em"/> <mml:msup> <mml:mrow> <mml:mo stretchy="false">(</mml:mo> </mml:mrow> <mml:mrow> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">Π</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>1</mml:mn> </mml:mrow> </mml:msub> <mml:mo stretchy="false">)</mml:mo> </mml:math> state, which allows for efficient population transfer between the ground state <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>X</mml:mi> <mml:mspace width="0.50em"/> <mml:msup> <mml:mrow> <mml:mo stretchy="false">(</mml:mo> </mml:mrow> <mml:mrow> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> <mml:msup> <mml:mrow> <mml:mi mathvariant="normal">Σ</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> </mml:mrow> </mml:msup> <mml:mo stretchy="false">)</mml:mo> </mml:math> and the Q state via <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>X</mml:mi> <mml:mo>−</mml:mo> <mml:mi>C</mml:mi> <mml:mo>−</mml:mo> <mml:mi>Q</mml:mi> </mml:math> 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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>X</mml:mi> <mml:mo>→</mml:mo> <mml:mi>C</mml:mi> </mml:math> transition dipole moment, and branching ratios of decays from the C state.