Scientists engineer molecular quantum registers with nitrogen-doped graphene

Scientists have made progress in designing molecular structures that could advance quantum computing. By modifying aza-triangulene—a type of nitrogen-doped nanographene—they created a three-qubit analogue with programmable spins. This breakthrough offers a new way to engineer quantum registers at the molecular level.

The study also revealed how nitrogen doping alters electronic and magnetic behaviour, enabling precise control over spin states in graphene-based systems.

The team began by redesigning aza-triangulene, transforming a single-radical molecule into a frustrated triradical system. They extended its structure with anthene units, producing correlated spins and a unique magnetic arrangement. This reconfiguration resulted in a molecular system resembling a three-qubit quantum register.

Unlike previous studies on nanographenes, the researchers used on-surface synthesis at room temperature on gold substrates. This approach allowed precise nitrogen doping, which enhanced spin localisation. Most earlier work relied on high-temperature ultra-high vacuum deposition or cryogenic scanning tunnelling microscopy (STM) techniques, often requiring temperatures as low as 4–5 K to observe Kondo effects.

Through computational modelling and advanced microscopy, they examined how nitrogen atoms alter graphene's electronic properties. The doping introduced magnetism, stabilising spin-polarised ground states at the molecule's zigzag edges. There, they detected a Kondo effect—a signature of strong electron-spin interactions—alongside a spin-1/2 ground state. Spectral analysis also revealed inelastic spin excitations, with Kondo temperatures around 3 K.

The findings demonstrate a practical method for engineering frustrated antiferromagnetic systems in aza-triangulene. By controlling chemical modifications, the team showed how to create and study these structures both in solution and on surfaces. Such open-shell nanographenes are now being explored for next-generation spintronics and quantum technologies.

The work provides a clear strategy for building molecular quantum registers with tunable spin properties. The room-temperature synthesis technique and nitrogen-doping method simplify the creation of complex magnetic states. These advances could support the development of scalable quantum computing components based on graphene architectures.