Strontium ions (blue) confined in a Paul trap
Sum-frequency generation @ 620nm
Linear Paul trap
Reference cavity for qubit laser
Reference cavity for qubit laser
Welcome to the Trapped Ion Quantum Technologies group led by Markus Hennrich. Our group is located at the Department of Physics at Stockholm University and is working on using trapped ions for quantum computation, quantum simulation and quantum sensing applications. In particular, we are one of only two groups worldwide that have realised trapped Rydberg ions - a promising technology for speeding up trapped ion quantum computers.
Our paper Electronic State-Dependent Conformational Changes in a Rydberg Ion Crystal has been published in PRL! M. Mallweger et al. Phys. Rev. Lett. 137, 063602 (2026). In this work we have used trapped ions to mimic the way molecules change shape when their electrons are excited, a process that is normally far too fast and complex to observe directly. By exciting a single ion at the centre of a three-ion crystal to a high-lying Rydberg state, we triggered a structural rearrangement of the crystal from a straight line into a zigzag, driven by the strong coupling between electronic and vibrational motion. The resulting mixing of electronic and vibrational states left a clear spectroscopic fingerprint, marking a first step toward using Rydberg ions to create and study artificial molecular systems.
We welcome two new group members. Jakub Dobosz and Yuhao Liu are joining us as postdocs.
Congratulations to Dr. Harry Parke, who successfully defended his PhD thesis on 26 May 2026! Harry has been a key member of our group and has made outstanding contributions to our research on trapped ion quantum technologies.
PhD thesis
We have submitted our manuscript R. Thomm, V. Shankar, N. Kuk, M. Mallweger, I. Straka, M. Hennrich, arXiv:2605.30483. We demonstrate coherent population transfer between Rydberg S and P states with 91.5% efficiency via microwave pulses, and create tunable dressed eigenstates with adjustable polarizability — from noise-resilient zero-polarizability states to strongly interacting ones.
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We have submitted our manuscript K. N. Zlatanov, M. Mallweger, M. Hennrich, N. V. Vitanov, arXiv:2604.13859. We propose a new pulse ordering that separates the STIRAP excitation and microwave dressing into distinct stages, eliminating interference and achieving a projected gate fidelity of 99.93% with a 400 ns gate time.
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We have submitted our manuscript W. S. Martins, M. Hennrich, F. Schmidt-Kaler, I. Lesanovsky, arXiv:2601.01626. We propose using Rydberg ions in a Penning trap to simulate 2D spin systems with MHz-scale coupling, enabling exploration of frustrated quantum dynamics and collective behaviour.
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