High-resolution 'magic'-field spectroscopy on trapped polyatomic molecules

TL;DR

This paper demonstrates high-resolution spectroscopy of trapped polyatomic molecules using a combination of electric trapping, a 'magic' field, and cooling techniques, achieving linewidths below 4 kHz and precise field control.

Contribution

It introduces a novel method combining microstructured electric traps, 'magic' field offsets, and optoelectrical cooling for high-resolution spectroscopy of polyatomic molecules.

Findings

Stark broadening reduced to below 1 kHz

Doppler-limited linewidths down to 3.8 kHz

'Magic'-field line position determined with <100 Hz uncertainty

Abstract

Rapid progress in cooling and trapping of molecules has enabled first experiments on high resolution spectroscopy of trapped diatomic molecules, promising unprecedented precision. Extending this work to polyatomic molecules provides unique opportunities due to more complex geometries and additional internal degrees of freedom. Here, this is achieved by combining a homogeneous-field microstructured electric trap, rotational transitions with minimal Stark broadening at a 'magic' offset electric field, and optoelectrical Sisyphus cooling of molecules to the low millikelvin temperature regime. We thereby reduce Stark broadening on the $J=5\leftarrow4$ ($K=3$) transition of formaldehyde at $364\,$GHz to well below $1\,$kHz, observe Doppler-limited linewidths down to $3.8\,$kHz, and determine the 'magic'-field line position with an uncertainty below $100\,$Hz. Our approach opens a multitude of possibilities for investigating diverse polyatomic molecule species.