Korea Research Institute of Standards and Science Develops Precise Single-Electron Energy Control Technology Using 'Chae'-Like Filter

Reducing Electron Instability and Stably Implementing Quantum States
Paving the Way for High-Performance Qubit Fabrication

The Korea Research Institute of Standards and Science (KRISS) has developed a technology that controls the energy of a single electron using a 'filter' similar to a 'chae' used in cooking.

This technology reduces the instability of electrons caused by external environments and can stably implement quantum states, making it a foundational technology expected to significantly enhance the performance of single-electron qubits (the basic units of information used to encode data in quantum computing).

Figure illustrating the research process. Provided by Korea Research Institute of Standards and Science (KRISS)

Electrons are fundamental particles that make up atoms. When the path of an electron is split, it exhibits quantum superposition, passing through two paths (0 and 1) simultaneously. Utilizing this characteristic for information processing enables the creation of qubits. Single-electron qubits are highly integrable, theoretically allowing dozens to be implemented in a small area, making them a promising technology for scaling up quantum computing.

However, improving the performance of single-electron qubits is challenging due to the electron's sensitivity to external environments. The performance of qubits depends on how accurately and stably quantum states are implemented, but electrons are very small and sensitive, making it difficult to realize quantum states. Their energy states become unstable due to interactions with the external environment or other electrons, causing them to easily lose their quantum properties.

The KRISS Quantum Device Group developed a technology that uses an 'energy filter' to control the energy form of single electrons as desired and reduce their instability.

The energy filter used by the research team is a conductive channel that, like a 'chae' used in cooking, allows only electrons with energy above a certain threshold to pass through while reflecting the rest.

The researchers first generated single electrons in a 'quantum dot,' an ultra-fine semiconductor structure that confines electrons. Then, by applying an appropriate voltage to a 'quantum point contact,' an ultra-fine conductive channel that controls electron flow, they formed an energy filter that selectively passes only high-energy electrons, successfully reducing the energy uncertainty of electrons by more than half.

Energy profile of a single electron confirmed by KRISS researchers using the Wigner distribution. Provided by KRISS

This technology is expected to be widely used in the development of single-electron-based quantum information processing technologies, including high-performance qubits. By removing unnecessary energy distributions and manipulating electrons only within a specific energy range, it not only stably implements the quantum phenomena of electrons but also minimizes interactions with the external environment and other electrons.

The research team also developed a technology to visualize the form of single electrons controlled by the energy filter on a two-dimensional graph.

They devised a method to compare the single-electron forms before and after passing through the energy filter using the 'Wigner distribution.' This allows intuitive confirmation of the time-energy information of single electrons, which changes depending on conditions, on a digital 2D graph, enabling detailed analysis of quantum characteristics of single electrons that were previously overlooked in experiments.

Myungho Bae, principal researcher of the KRISS Quantum Device Group, said, "This achievement will contribute to significantly enhancing the practical applicability of quantum information technology based on single electrons."

This research was conducted in collaboration with Professor Jujin Kim of Jeonbuk National University, Professor Heungseon Shim of the Korea Advanced Institute of Science and Technology, and principal researcher Jindong Song of the Korea Institute of Science and Technology. It was supported by the National Research Foundation of Korea's Mid-career Researcher Support Program and KRISS's Basic Research Project. The research results were published in Nano Letters (IF: 9.6) in October last year.

◇ Wigner Distribution: A method that visually analyzes the quantum state of electrons by converting it into a function distribution of time (position) and energy (momentum). In this experiment, the research team compared changes in the energy of single electrons using the Wigner distribution and developed a technology to convert it into digital signals for precise analysis.

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