Simon Roggors · Thomas Unden · Anna Aubele · Paul Mentzel · Gregor Bayer · Alon Salhov · Jochen Scharpf · Martin B. Plenio · Alex Retzker · Fedor Jelezko · Tim R. Eichhorn · Tobias A. Schaub · matthias Pfender · Philipp Neumann · Ilai Schwartz

Nature · 2026

Optical interfaces that connect long-lived spin qubits to photons are a central requirement for quantum networking and distributed quantum information processing. At present, solid-state atomic defects are leading candidates because of their inherent spin and optical coherence. Building on these advancements, synthetically tailored molecular systems represent a fundamental change in the field, using precise atomic control and consistent bottom-up assembly. However, a molecular platform that concurrently satisfies the demands of a robust spin–photon interface—namely, the combination of bright fluorescence, high spectral stability and long ground-state spin lifetimes—has yet to be realized at the single-molecule level. Here we show that a triplet ground-state carbene molecule, embedded within a structurally matched host crystal, functions as a robust spin–photon interface with single-molecule addressability. The system exhibits narrow ZPLs, spectral stability over more than an hour, spin-selective optical transitions and single-molecule optically detected magnetic resonance. Coherent control yields millisecond-scale dynamical-decoupling coherence and tens-of-milliseconds spin relaxation at a temperature of 4.5 K. These results establish molecular qubits as a viable platform for single-emitter quantum optics while preserving the advantages of bottom-up chemical design and processable materials.

Nature (2026)
https://doi.org/10.1038/s41586-026-11147-6

Nature · Creative Commons BY 4.0