Researchers at Karlsruhe Institute of Technology (KIT) and the Centre National de la Recherche Scientifique (CNRS) in Grenoble and Strasbourg have taken an important step toward realizing a quantum computer. Using a spin cascade in a single-molecule magnet, the scientists demonstrated how nuclear spins can be manipulated with electric fields. Such electric field manipulation allows for quick and specific switching of quantum bits. The experimental results were reported in the June 6 issue of Science (DOI: 10.1126/science.1249802; p. 1135).

One of the most ambitious goals of nanotechnology is to realize a quantum computer. Such a computer, which is based on the principles of quantum mechanics, is expected to perform tasks much more efficiently than a classic computer. A quantum computer uses so-called quantum bit, or “qubit,” as the smallest computation unit. Qubits can rely on nuclear spins. Interlinkage of qubits with each other results in mixed quantum states, which can be used to execute many calculation steps in parallel.

The KIT and CNRS researchers have manipulated a single nuclear spin purely using an electric field. “Use of electric instead of magnetic fields paves the way to addressing quantum states in conventional electronic circuits,” said Mario Ruben, head of the Molecular Materials Research Group of KIT’s Institute of Nanotechnology (INT). “There, quantum states can be manipulated specifically by so-called displacement currents. Then, they can be directly read out electronically.”

For their experiments, the researchers used a nuclear spin-qubit transistor consisting of a single-molecule magnet connected to three electrodes (source, drain, and gate). The single-molecule magnet was a TbPc₂ molecule—a single metal ion of terbium that is enclosed by organic phthalocyanine molecules of carbon, nitrogen, and hydrogen atoms. The gap between the electric field and the spin is bridged by the so-called hyperfine-Stark effect that transforms the electric field into a local magnetic field. This quantum mechanics process can be transferred to all nuclear spin systems and, hence, opens up the possibility of integrating quantum effects in nuclear spins into electronic circuits.