Precision frequency-comb terahertz spectroscopy on pure quantum states of a single molecular ion

TL;DR

This paper demonstrates high-precision terahertz spectroscopy on a single quantum state of a molecular ion using quantum-logic techniques, achieving unprecedented resolution and enabling detailed molecular studies.

Contribution

It introduces a quantum-logic-based method for preparing, manipulating, and reading out single molecular ion states with high precision, surpassing traditional ensemble spectroscopy limitations.

Findings

Resolved rotational transitions to 11 significant digits

Derived the rotational constant of CaH+ with high accuracy

Applicable to a wide range of molecular ions

Abstract

Spectroscopy is a powerful tool for studying molecules and is commonly performed on large thermal molecular ensembles that are perturbed by motional shifts and interactions with the environment and one another, resulting in convoluted spectra and limited resolution. Here, we use generally applicable quantum-logic techniques to prepare a trapped molecular ion in a single quantum state, drive terahertz rotational transitions with an optical frequency comb, and read out the final state non-destructively, leaving the molecule ready for further manipulation. We resolve rotational transitions to 11 significant digits and derive the rotational constant of CaH+ to be B_R = 142501777.9(1.7) kHz. Our approach suits a wide range of molecular ions, including polyatomics and species relevant for tests of fundamental physics, chemistry, and astrophysics.