Quantum computers have the potential to solve certain calculations exponentially faster than a classic computer could, but more research is desperately needed to make their practical use a reality. Quantum computers use a basic unit of information called quantum bits (qubits) to run - like how classical computers use a binary system of 0s and 1s, but with many more possibilities. However, a large number of qubits are required for quantum computers to function. Research into quantum dots - nanostructures with unique properties that allow them to serve as qubits - is crucial to overcoming this roadblock.

Researchers at the Advanced Institute for Materials Research (WPI-AIMR), Tohoku University, have made a significant step toward the realization of next-generation quantum information processing technologies. In this study, the research team successfully created and electrically controlled triple quantum dots in zinc oxide (ZnO), an oxide semiconductor known for its good spin coherence and strong electron correlations. While single and double quantum dots in ZnO have been previously demonstrated, scaling up to multiple, controllable dots has remained a major challenge until now. By coupling multiple quantum dots, researchers can study complex quantum behaviors and develop potential architectures for quantum computation.

The team also observed a unique phenomenon known as the quantum cellular automata (QCA) effect, which emerges only in systems composed of three or more coupled quantum dots.

The research team, led by Associate Professor Tomohiro Otsuka at WPI-AIMR and the Research Institute of Electrical Communication, Tohoku University, fabricated a ZnO heterostructure device capable of forming three coupled quantum dots through precise electric-field control. They confirmed that each quantum dot reached a few-electron regime, a crucial condition for the application of quantum bits. Furthermore, by analyzing electron transport characteristics, the researchers detected the QCA effect, in which the charge configuration in one quantum dot influences the neighboring dots through electrostatic coupling and induces simultaneous movement of two electrons -- a key mechanism envisioned for low-power quantum logic operations.

"This study shows that ZnO can host multiple, well-controlled quantum dots where complex quantum interactions occur," said Otsuka. "Our next step is to explore coherent quantum control and qubit operations in these oxide systems."

This research opens a new pathway by using ZnO -- a material already familiar from everyday technologies like sunscreens and transparent electronics -- to create and control quantum bits. This type of research is an important step towards overcoming the major challenges of building stable and scalable quantum systems. If we can achieve this, quantum computers promise to revolutionize fields such as materials design, drug discovery, and data security. Therefore, this discovery not only expands the range of materials available for quantum computing, but also moves us closer to practical, energy-efficient quantum devices in the future.

This study was published online in Scientific Reports on October 21, 2025.

Publication Details:

Title: Formation of few-electron triple quantum dots in ZnO heterostructures

Authors: Koichi Baba, Kosuke Noro, Yusuke Kozuka, Takeshi Kumasaka, Motoya Shinozaki, Masashi Kawasaki, and Tomohiro Otsuka

Journal: Scientific Reports

DOI: https://doi.org/10.1038/s41598-025-20567-9

Press release in Japanese