Scientists control nuclear spins in molecular crystal with lasers

Laser pulses and radio-frequency fields have now been used to initialize, steer and read out nuclear spin states inside a europium-based molecular crystal, a step that pushes molecular quantum hardware closer to something engineers could actually build on.

Researchers at Karlsruhe Institute of Technology said they achieved the first optical initialization, control and detection of nuclear spin states in a molecular material. The system uses ultranarrow optical transitions in europium ions, which let the team address the nuclear spins directly without interference from electron spins. That matters because nuclear spins are among the strongest candidates for quantum information storage: they are naturally isolated from much of their environment, which helps them hold quantum states longer than many other platforms.

The experiment, described in Nature Materials on March 19, 2026, under the title “Optically detected nuclear magnetic resonance of coherent spins in a molecular complex,” involved a europium-based molecular crystal synthesized by Mario Ruben’s group at KIT. The authors, including Evgenij Vasilenko, Vishnu Unni Chorakkunnath, Jeremias Resch, Nicholas Jobbitt, Diana Serrano, Philippe Goldner, Senthil Kumar Kuppusamy, Mario Ruben and David Hunger, addressed two nuclear quadrupole resonances and used Rabi oscillations, spin echo and dynamical decoupling to extend nuclear spin coherence to as long as 2 milliseconds.

That is still a laboratory-scale result, not a device ready for deployment. But 2 milliseconds is a meaningful benchmark for any qubit platform, and the paper points to a practical payoff that reaches beyond quantum computing. The same approach could improve nuclear magnetic resonance signals at low magnetic field and could eventually push sensitivity down to the single-molecule level, while the molecular format offers something solid-state systems often struggle to match: chemically tailored structures with atomically precise spacing.

David Hunger said the results show that molecular materials can be a promising platform for future quantum components, and he highlighted the advantage of addressing nuclear spins without electron-spin interference. That combination could help build denser qubit registers if the readout, control and fabrication hurdles can be solved at scale.

The new work also builds on earlier KIT and partner results that had already made europium molecular crystals look unusually promising. In 2021, collaborators from KIT, Chimie ParisTech, CNRS and the European Center for Quantum Sciences reported efficient polarization of ground-state nuclear spins in a binuclear Eu(III) complex, with a ground-state spin population lifetime of 1.6 ± 0.4 seconds at 1.4 K. KIT later reported optical linewidths in the tens of kilohertz range, and in 2022 said europium ions in molecules can couple via electric stray fields, a route toward future entanglement and high qubit density. The latest result turns those earlier pieces into a full optical control demonstration, but the gap from molecular proof-of-principle to a usable quantum component remains wide.