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Researchers from the Institute of Industrial Science, The University of Tokyo have solved a foundational problem in transmitting quantum information, which could dramatically enhance the utility of integrated circuits and quantum computing. Credit: Institute of Industrial Science, The University of Tokyo

Quantum electronics represents a significant departure from conventional electronics. In traditional systems, memory is stored in binary digits. In contrast, quantum electronics utilizes qubits for storage, which can assume various forms, including electrons trapped in nanostructures known as quantum dots. Nonetheless, the ability to transmit information beyond the adjacent quantum dot poses a substantial challenge, thereby limiting the design possibilities for qubits.

Now, in a study recently published in Physical Review Letters, researchers from the Institute of Industrial Science at the University of Tokyo are solving this problem: they developed a new technology for transmitting quantum information over perhaps tens to a hundred micrometers. This advance could improve the functionality of upcoming quantum electronics.

How can researchers transmit quantum information, from one quantum dot to another, on the same quantum computer chip? One way might be to convert electron (matter) information into light (electromagnetic wave) information: by generating lightmatter hybrid states. Previous work has been incompatible with the one-electron needs of quantum information processing. Improving on high-speed quantum information transmission in a way that is more flexible in design and is compatible with the semiconductor fabrication tools that are currently available was the goal of the research teams study.

In our work, we couple a few electrons in the quantum dot to an electrical circuit known as a terahertz split-ring resonator, explains Kazuyuki Kuroyama, lead author of the study. The design is simple and suitable for large-scale integration.

Previous work has been based on coupling the resonator with an ensemble of thousands to tens of thousands of electrons. In fact, the coupling strength is based on the large size of this ensemble. In contrast, the present system confines only a few electrons, which is suitable for quantum information processing. Nevertheless, both electrons and terahertz electromagnetic waves are confined to an ultra-small area. Therefore, the coupling strength is comparable in strength to that of many-electron systems.

Were excited because we use structures that are widespread in advanced nanotechnology and are commonly integrated into semiconductor manufacturing to help solve a practical quantum information transmission problem, says Kazuhiko Hirakawa, senior author. We also look forward to applying our findings to understanding the fundamental physics of lightelectron coupled states.

This work is an important step forward in solving a previously vexing problem in transmitting quantum information that has limited applications of laboratory findings. In addition, such lightmatter interconversion is regarded as one of the essential architectures for large-scale quantum computers based on semiconductor quantum dots. Because the researchers results are based on materials and procedures that are common in semiconductor manufacturing, practical implementation should be straightforward.

Reference: Coherent Interaction of a Few-Electron Quantum Dot with a Terahertz Optical Resonator by Kazuyuki Kuroyama, Jinkwan Kwoen, Yasuhiko Arakawa and Kazuhiko Hirakawa, 9 February 2024, Physical Review Letters. DOI: 10.1103/PhysRevLett.132.066901

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