The road to new quantum devices: electrically defined quantum dots in zinc oxide

Researchers have successfully created electrically defined quantum dots within zinc oxide (ZnO) heterostructures, marking an important milestone in the development of quantum technology.

Details of their breakthrough were published in the journal Nature Communications on November 7, 2024.

Quantum dots, small semiconductor structures that can trap electrons in nanometer-scale spaces, have been studied for years for their potential to function as qubits in quantum computing. These dots are critical to quantum computing because they allow scientists to control the behavior of electrons, much like a conductor controls the flow of water through a pipe.

To date, most research has focused on materials such as gallium arsenide (GaAs) and silicon. However, zinc oxide, a material known for its strong electronic correlation and excellent spin-quantum coherence, has been proposed for use in electrically defined quantum dots, that is, quantum dots that are created and controlled using electrical methods. It had not been studied yet.

In this study, the research team was able to manipulate the internal states of quantum dots within zinc oxide using precise voltage control, much like adjusting the dial on a radio to fine-tune the signal. I did. This innovation made it possible to observe Coulomb diamonds, a key property of quantum dots, and provided insight into the behavior of electrons trapped inside.

“Coulomb diamonds are like fingerprints that help identify the unique ‘personality’ of each quantum dot,” says Tomohiro Otsuka, associate professor at Tohoku University and corresponding author of the paper. “By using zinc oxide, we are breaking new ground in developing efficient and stable qubits that are the basis of quantum computing.”

One of the most notable findings of this study was the discovery of the Kondo effect in zinc oxide quantum dots. The Kondo effect is a quantum phenomenon in which electronic interactions cause conduction, which typically depends on the number of electrons in the quantum dot. However, in zinc oxide, the researchers observed this effect even when the number of electrons did not fit the usual pattern. This new behavior is related to the material’s strong electronic correlation and adds further complexity and potential to zinc oxide-based quantum devices.

“The Kondo effect we observed is different from what is typically seen in other semiconductors such as GaAs,” Otsuka added. “This difference could help us better understand the behavior of electrons in this new material and improve our ability to control and manipulate qubits.”

Looking ahead, the team is focused on leveraging these new discoveries to develop practical quantum devices.