A discovery of electrically controlled triple quantum dots in zinc oxide by the Advanced Institute for Materials Research (WPI-AIMR), Tohoku University, moves us closer to energy-efficient quantum devices can be used practically.
(a) The schematic of the fabricated ZnO device. Two-dimensional electron gas is formed between (Mg, Zn)O and ZnO. Quantum dots are formed by applying gate voltage to this two-dimensional electron gas. (b) Scanning electron microscope image of the device. The triple quantum dots are formed in the lower half, and the sensor quantum dot and quantum point contact are formed in upper half.
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.
White characters in figure show the number of electrons in each quantum dots. (a) Observed charge stability diagram. Three different slopes of the charge transition lines indicate formation of triple quantum dots. No transition line is observed in the lower left regime, which suggests these quantum dots are in few-electron regime. (b) QCA effect observed in ZnO quantum dots. Two electrons move at the same time when the number of electron changes from 022 to 113.
Published: 14 Nov 2025
Contact details:
Tohoku University Public Relations Division 2-1-1, Katahira, Aoba-ku, Sendai, 980-8577
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
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