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Electronic State-Dependent Conformational Changes in a Rydberg Ion Crystal

Marion Mallweger1,*, Natalia Kuk1, Vinay Shankar1, Robin Thomm1, Harry Parke1, Ivo Straka1, Weibin Li2, Igor Lesanovsky2,3, and Markus Hennrich1,†

  • 1Department of Physics, Stockholm University, 10691 Stockholm, Sweden
  • 2School of Physics and Astronomy and Centre for the Mathematics and Theoretical Physics of Quantum Non-Equilibrium Systems, University of Nottingham, Nottingham NG7 2RD, United Kingdom
  • 3Institut für Theoretische Physik and Center for Integrated Quantum Science and Technology, Universität Tübingen, Auf der Morgenstelle 14, 72076 Tübingen, Germany

  • *Contact author: marion.mallweger@physics.ox.ac.uk
  • †Contact author: markus.hennrich@fysik.su.se
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Phys. Rev. Lett. 137, 063602 – Published 6 August, 2026

DOI: https://doi.org/10.1103/1bqh-pmgz

Abstract

State-dependent conformational changes play a central role in molecular dynamics, yet they are often difficult to observe or simulate due to their complexity and ultrafast nature. One alternative approach is to emulate such phenomena using quantum simulations with cold, trapped ions. In their electronic ground state, these ions form long-lived Wigner crystals. When excited to high-lying electronic Rydberg states, the ions experience a modified trapping potential, resulting in a strong coupling between their electronic and vibrational degrees of freedom. In an ion crystal, this vibronic coupling creates electronic state-dependent potential energy surfaces that can support distinct crystal structures—closely resembling the conformational changes of molecules driven by electronic excitations. Here, we present the first experimental observation of this effect, by laser coupling a single ion at the center of a three-ion crystal to a Rydberg state. By tuning the system close to a structural phase transition, the excitation induces a state-dependent conformational change, transforming the Wigner crystal from a linear to a zigzag configuration. This structural change leads to a strong hybridization between vibrational and electronic states, producing a clear spectroscopic signature in the Rydberg excitation. Our findings mark the first experimental step toward using Rydberg ions to create and study artificial molecular systems.

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Phys. Rev. Lett. 137, 063602– Published 6 August, 2026
  • Received 2 November 2025
  • Accepted 14 May 2026
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