![Core structure of Co₃(dpa)₄Cl₂ with the schematic illustration of spin qubit. Credit: Sekine et al.]

Researchers at Kumamoto University, in collaboration with colleagues in South Korea and Taiwan, have discovered that a unique cobalt‑based molecule with metal–metal bonds can function as a spin quantum bit (spin qubit)—a fundamental unit for future quantum computers. The findings provide a new design strategy for molecular materials used in quantum information technologies.

The study is published in the journal Chemical Communications.

Quantum computing and spin qubits

Quantum computers process information using quantum bits, or qubits, which can exist in multiple states at the same time. Among various approaches, spin qubits, which use the spin of an electron, are especially attractive because they can be precisely controlled using magnetic resonance techniques. However, creating stable and long‑lived spin qubits at the molecular level has remained a major challenge.

The research team focused on a rigid molecule composed of three cobalt ions aligned in a straight line and directly connected by metal–metal bonds. This compound, known as Co₃(dpa)₄Cl₂, is also a “spin‑crossover” material, meaning its spin state can change in response to external conditions such as temperature. Until now, whether such a molecule could serve as a spin qubit had not been experimentally confirmed.

Experimental findings and implications

Using advanced magnetic measurements and pulsed electron paramagnetic resonance (EPR) spectroscopy, the researchers closely examined how long the electron spins in the molecule can maintain their quantum state. They found that the molecule exhibits slow magnetic relaxation, with spin lifetimes long enough to meet key requirements for quantum information processing. Importantly, the electron spin is not confined to a single metal atom but is delocalized across all three cobalt ions, which helps stabilize the quantum state.

The team also observed clear Rabi oscillations, a hallmark of controlled quantum behavior, demonstrating that the spin states can be coherently manipulated. These results show, for the first time, that a molecule with metal–metal bonds can act as a functional spin qubit.

“This work opens a new pathway for designing molecular qubits,” said Professor Shinya Hayami (Faculty of Advanced Science and Technology, Kumamoto University), who led the study. “By using rigid, multinuclear metal complexes, we can suppress unwanted vibrations and achieve longer spin lifetimes.”

The researchers expect their findings to accelerate the development of molecular‑based quantum materials, with potential applications in quantum computing, quantum memory, and spin‑based electronics.