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arXiv:2507.11487 · Physical Review A

Microwave spectroscopy and multichannel quantum defect analysis of ytterbium 6 s n p , 6 s n f , and 6 s n g Rydberg states

Rin Kuroda, Vernon M. Hughes, Martin Poitrinal, Michael Peper, Jeff D. Thompson

Published Sep 16, 2025• 2 citations
arXivHTMLPDF

Abstract

The complex Rydberg structure of ytterbium atoms is shaped by multiple low-lying ion-core-excited states and strong channel interactions, which presents both opportunities and challenges for quantum information processing and precision metrology. In this work, we extend high-resolution microwave spectroscopy and multichannel quantum defect theory (MQDT) modeling of singly excited $6sn\ensuremath{\ell}$ Rydberg states in $^{174}\mathrm{Yb}$ and $^{171}\mathrm{Yb}$ to include the $\ensuremath{\ell}=3$ ($f$) and $\ensuremath{\ell}=4$ ($g$) series. Our measurements reveal $p\text{\ensuremath{-}}f$ mixing in odd-parity Rydberg states of $^{171}\mathrm{Yb}$, which we incorporate by combined MQDT models for $6snp$ and $6snf$ series. Additionally, we observe that for $\ensuremath{\ell}=4$ the spin-orbit interaction dominates over the exchange interaction, such that the $6sng$ states are more accurately described in a $jj$-coupled basis. We validate our models by comparing the predicted Land\'e $g$ factors and static dipole polarizabilities with experimental measurements, finding excellent agreement. These results provide important input for designing high-fidelity entangling gates with ytterbium atoms.

DOI
10.1103/mzsv-rckx

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Highly excited Rydberg states and their interactions play an important role in quantum computing and simulation. These properties can be predicted accurately for alkali atoms with simple Rydberg level structures. However, an extension of these methods to more complex atoms such as alkaline-earth atoms has not been demonstrated or experimentally validated. Here, we present multichannel quantum defect models for highly excited Yb 174 and Yb 171 Rydberg states with L ≤ 2 . The models are developed using a combination of existing literature data and new, high-precision laser and microwave spectroscopy in an atomic beam, and validated by detailed comparison with experimentally measured Stark shifts and magnetic moments. We then use these models to compute interaction potentials between two Yb atoms, and find excellent agreement with direct measurements in an optical tweezer array. From the computed interaction potential, we identify an anomalous Förster resonance that likely degraded the fidelity of previous entangling gates in Yb 171 using F = 3 / 2 Rydberg states. We then identify a more suitable F = 1 / 2 state, and achieve a state-of-the-art controlled- gate fidelity of F = 0.994 ( 1 ) , with the remaining error fully explained by known sources. This work establishes a solid foundation for the continued development of quantum computing, simulation, and entanglement-enhanced metrology with Yb neutral atom arrays.
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The MQDT of hyperfine structure is greatly simplified in extremely high Rydberg states. A four (or three)-channel quantum defect model is derived for the hyperfine structure of extremely high Rydberg states of msnd configuration in odd alkaline-earth isotopes, in which the transformation matrix U i(F)i' is given analytically except for one parameter which measures the mixing of singlet 1 D 2 and triple 3 D 2 induced by spin-orbit interaction in even isotopes, and in which the four eigen quantum defects mu i' (i'=1, 2, 3, 4) are related to the quantum defects of the fine structure in even isotopes by mu i' =mod( delta i' ). This model has been used to interpret the observed sublevel structure of 5snd (n>100) configurations in 87 Sr. An excellent agreement between the theoretical and experimental results was achieved.
Abstract In this work, we present a comprehensive experimental investigation of the isotope dependence of the binding energies of S - and D -Rydberg states in ytterbium. Using two-photon excitation via the intermediate 6 s 6 p 1 P 1 state in a magneto-optical trap, we measured excitation energies for the bosonic isotopes 172 Yb, 174 Yb, and 176 Yb, as well as for the fermionic isotopes 171 Yb ( I = 1 / 2 ) and 173 Yb ( I = 5 / 2 ), covering principal quantum numbers in the range 35 ⩽ n ⩽ 80 . For the bosonic isotopes, the isotope shifts are found to be independent of n , consistent with a single-channel quantum defect model. For 171 Yb, our results confirm previous high-precision measurements and multi-channel quantum defect modeling reported by Peper et al (2025), while for 173 Yb we provide the first detailed Rydberg spectra, revealing a complex level structure consistent with strong hyperfine-induced channel mixing and clear
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^{174}174Yb in 6sns 1S06sns\,^1S_06sns1S0​ Rydberg states across nearly two decades in principal quantum number nnn 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 sss-wave scattering length and the positions of two spin-orbit split ppp-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 determine the quantum defect of the 6s23f 1F36s23f\, ^1F_36s23f1F3​ state. 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.