A significant leap in the field of quantum technology has been achieved with the successful creation of electrically manipulated quantum dots within zinc oxide (ZnO) heterostructures. The details of this breakthrough, published in Nature Communications on November 7, 2024, bring us one step closer to the realization of quantum computing.

Quantum dots are minuscule structures within semiconductors that can confine electrons within incredibly small spaces, measured in nanometers. These structures are essential in quantum computing due to their ability to regulate electron behavior, much like a conductor controlling the flow of water in pipes.

Until recently, the majority of research concentrated on materials like gallium arsenide (GaAs) and silicon. However, zinc oxide, a material recognized for its strong electron correlation and superior spin quantum coherence, had not been used in the formation and control of quantum dots using electrical means.

In this groundbreaking study, the researchers were able to fine-tune the internal states of zinc oxide’s quantum dots using precise voltage control, akin to adjusting a radio’s dials to perfect its signal. This innovative approach enabled the observation of the Coulomb diamond, a key trait of quantum dots. This breakthrough provides deeper insights into the behavior of confined electrons.

“The Coulomb diamond acts as a unique identifier for each quantum dot, much like a fingerprint”, explains Tomohiro Otsuka, an associate professor at Tohoku University and one of the paper’s authors. “By employing zinc oxide, we’re pioneering new possibilities in creating efficient and stable qubits, the building blocks of quantum computing.”

Perhaps the most striking discovery of the study was the manifestation of the Kondo effect within zinc oxide quantum dots. The Kondo effect, a quantum phenomenon where electron interactions result in conduction, usually relies on the number of electrons in the quantum dot. Surprisingly, this effect was observed in zinc oxide even when the electron count didn’t follow the regular pattern. This unique behavior, associated with the material’s strong electron correlation, adds an additional layer of potential to zinc oxide-based quantum devices.

“The Kondo effect we observed differs from what we typically see in other semiconductors like GaAs”, notes Otsuka. “This variance may enhance our understanding of electron behavior in this novel material and improve our capability to control and manipulate qubits.”

Moving forward, the team is committed to leveraging these new discoveries to create practical quantum devices.