Enroute to a quantum computer

The Volkswagen Foundation is financing a materials science project being conducted jointly by the universities in Mainz and Osnabrück in collaboration with the Jülich Research Center. The support is to be provided over a period of three years and will total €550,000.

The project managers, Professor Dr. Angelika Kühnle and Dr. Wolfgang Harneit of the Institute of Physical Chemistry at Johannes Gutenberg University Mainz (JGU), were notified of the grant in March 2012. This project is a continuation of a recently completed earlier project that was also financed by the Volkswagen Foundation.

The overall objective of the projects is to demonstrate the technical feasibility of a quantum computer on the basis of electron spins. Quantum computers are theoretically capable of far more efficient calculations than those of today's silicon-based computers. However, the necessary materials that would make quantum computers suitable for everyday use have yet to be invented.

For its experiments, the project team working under Kühnle and Harneit is using special fullerenes, soccer ball-shaped carbon molecules with enclosed nitrogen atoms. The electron spin of this nitrogen atom serves as a qubit, the quantum equivalent of the classic silicon-based computer bit. To read these qubits, the scientists have to insert the fullerenes in diamond nitrogen-vacancy centers, i.e., point defects in the diamond lattice, which can be scanned optically. It was Wolfgang Harneit who originated the idea of using fullerenes as qubits and who set out the original concepts in 2002.

In the first project, the researchers confirmed that the results of quantum calculations using fullerenes could be read with the aid of nitrogen-vacancy centers in diamonds. However, as the fullerenes failed to configure appropriately in the diamonds, it was not possible to perform coherent calculations. In the second project, the researchers plan to attach the fullerenes to carbon nanotubes and then insert these in diamonds. The resulting configuration should then make it possible to perform intelligible complex quantum calculations.

“We are working on quantum computers that are scalable because we are at the limits of silicon technology,” says Angelika Kühnle. “A quantum computer is a completely revolutionary type of computer and a successful implementation would have impressive capacity.” The current project is entitled “Spin quantum computing based on endohedral fullerenes with integrated single-spin read-out via nitrogen vacancy centers in diamond.” It will be sponsored through the Volkswagen Foundation's “Integration of Molecular Components in Functional Macroscopic Systems” program, just like its predecessor.

Angelika Kühnle's research makes her an important contributor to the Molecularly Controlled Non-Equilibrium (MCNE) Cluster of Excellence at JGU, which is currently competing in the final round of Germany's Federal Excellence Initiative.