Revealing Electron-Ytterbium Interactions through Rydberg Molecular Spectroscopy

TL;DR

This study combines experimental and theoretical approaches to explore ultralong-range Rydberg molecules of ytterbium, revealing detailed electron-ytterbium interactions and refining atomic parameters, thus advancing divalent atom research.

Contribution

It provides the first comprehensive analysis of Yb Rydberg molecules, including potential calculations, scattering phase shifts, and quantum defect refinements, establishing a foundation for future divalent atom experiments.

Findings

Quantitative agreement between theory and high-resolution spectra.

Extraction of electron-Yb scattering phase shifts and scattering length.

Refined the quantum defect for the $6s23f$ state.

Abstract

Divalent atoms have emerged as powerful alternatives to alkalis in ultracold atom platforms, offering unique advantages arising from their two-electron structure. Among these species, ytterbium (Yb) is especially promising, yet its anionic properties and its Rydberg spectrum remain comparatively unexplored. In this work, we perform a first and comprehensive experimental and theoretical investigation of ultralong-range Rydberg molecules (ULRMs) of $^{174}$Yb in $6sns\,^1S_0$ Rydberg states across nearly two decades in principal quantum number $n$ and three orders of magnitude in molecular binding energy. Using the Coulomb Green's function formalism, we compute Born-Oppenheimer molecular potentials describing the Rydberg atom in the presence of a ground-state perturber and achieve quantitative agreement with high-resolution molecular spectra. This enables the extraction of low-energy electron-Yb scattering phase shifts, including the zero-energy $s$-wave scattering length and the positions of two spin-orbit split $p$-wave shape resonances. Our results provide strong evidence that the Yb$^{-}$ anion exists only as a metastable resonance. We additionally show the sensitivity of ULRM spectra to the atomic quantum defects, using this to refine the value for the $6s23f\, ^1F_3$ quantum defect. Together, these findings establish Yb ULRMs as a powerful probe of electron-Yb interactions and lay essential groundwork for future Rydberg experiments with divalent atoms.