Narrowline Laser Cooling and Spectroscopy of Molecules via Stark States

The electronic energy level structure of yttrium monoxide (YO) provides a long-lived, low-lying <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:msup> <a:mi/> <a:mn>2</a:mn> </a:msup> <a:mi mathvariant="normal">Δ</a:mi> </a:math> state ideal for high-precision molecular spectroscopy, narrowline laser cooling at the single photon-recoil limit, and studying dipolar physics with unprecedented interaction strength. High-resolution laser spectroscopy of ultracold laser-cooled YO molecules is used to study the Stark effect in the <d:math xmlns:d="http://www.w3.org/1998/Math/MathML" display="inline"> <d:msup> <d:mrow> <d:mi mathvariant="normal">A</d:mi> </d:mrow> <d:mrow> <d:mi mathvariant="normal">′</d:mi> </d:mrow> </d:msup> <d:msup> <d:mspace width="0.1em"/> <d:mn>2</d:mn> </d:msup> <d:msub> <d:mi mathvariant="normal">Δ</d:mi> <d:mrow> <d:mn>3</d:mn> <d:mo>/</d:mo> <d:mn>2</d:mn> </d:mrow> </d:msub> <d:mspace width="0.2em"/> <d:mi>J</d:mi> <d:mo>=</d:mo> <d:mn>3</d:mn> <d:mo>/</d:mo> <d:mn>2</d:mn> </d:math> state. An immediate onset of the linear Stark effect is observed in the presence of weak applied electric fields due to the near-degenerate <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline"> <k:mi mathvariant="normal">Λ</k:mi> </k:math> doublet and the large electric dipole moment. By applying a small electric field the Stark-insensitive state is spectroscopically isolated and the absolute transition frequency to the <n:math xmlns:n="http://www.w3.org/1998/Math/MathML" display="inline"> <n:mrow> <n:mi mathvariant="normal">X</n:mi> </n:mrow> <n:msup> <n:mspace width="0.1em"/> <n:mn>2</n:mn> </n:msup> <n:msup> <n:mi mathvariant="normal">Σ</n:mi> <n:mo>+</n:mo> </n:msup> </n:math> electronic ground state is determined with a fractional frequency uncertainty of <s:math xmlns:s="http://www.w3.org/1998/Math/MathML" display="inline"> <s:mn>9</s:mn> <s:mo>×</s:mo> <s:msup> <s:mn>10</s:mn> <s:mrow> <s:mo>−</s:mo> <s:mn>12</s:mn> </s:mrow> </s:msup> </s:math> . This electric field control is necessary to implement a quasi-closed photon-cycling scheme that preserves parity. With this scheme the first narrowline laser cooling of a molecule is demonstrated, reducing the temperature of sub-Doppler cooled YO in two dimensions.