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Observation of Spin-Singlet Butterfly Rydberg Molecules in an Ultracold Atomic Rb Gas

Markus Exner1, Rohan Srikumar2, Richard Blättner1, Peter Schmelcher2,3, H. R. Sadeghpour4, Matthew T. Eiles5,6, and Herwig Ott1,*

  • *Contact author: ott@physik.uni-kl.de
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Phys. Rev. Lett. 136, 243002 – Published 18 June, 2026

DOI: https://doi.org/10.1103/q5r1-whjr

Abstract

We report the observation of spin-singlet ultralong-range Rydberg butterfly molecules consisting of a ground-state atom bound to a Rydberg atom by P-wave scattering of Rb87 Rydberg electrons from Rb87(5  s) atoms. A three-photon excitation scheme enables the photoassociation of these molecules by weakly admixing Rb(18f7/2) states. The measured binding energies, kilo-Debye permanent electric dipole moments, and lifetimes are in excellent agreement with theory. Two long-lived vibrational levels, red detuned from the Rb(18f7/2) threshold, are observed. This experiment is a foundational step in the production of ultracold anions and heavy Rydberg ion-pair systems.

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Phys. Rev. Lett. 136, 243002– Published 18 June, 2026
  • Received 30 November 2025
  • Accepted 4 May 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

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