A group research project from the Quantum Device Lab at the School of Electrical Engineering, KAIST, led by Professor Young-Ik Sohn, has been selected as a new 2025 project under the Quantum Science and Technology Flagship Program. The project is titled “All-Photonic Quantum Repeaters Based on Chip-Scale Fusion Multiplexing and Quantum-Dot-Based Deterministic Linear Cluster States.”
This research aims to develop quantum repeaters, a core enabling system essential for long-distance quantum communication. In particular, it distinguishes itself from conventional approaches by pursuing an all-photonic quantum repeater, which relies exclusively on photonic qubits without employing matter-based qubits such as electron spins. The all-photonic quantum repeater is an emerging research paradigm whose theoretical foundation has only recently been established, and it is gaining significant attention as a key candidate technology for next-generation quantum networks.
The conceptual architecture of an all-photonic quantum repeater consists of repeated units composed of a Repeater Graph State (RGS) node, which generates entangled photons, and a measurement node.
By eliminating matter-based qubits, this novel approach offers a crucial advantage: the potential for large-scale manufacturing using only existing semiconductor fabrication technologies. As a result, the proposed technology is considered to possess strong potential to evolve into an industry-standard quantum repeater platform in the future.
To achieve these ambitious research objectives, an industry–academia consortium has been formed, led by KAIST and joined by domestic component companies Fiberpro and Quad. In addition, an international collaborative research team has been established with Quandela, a world-leading French photonic quantum computing company. The Quandela research team will closely collaborate to apply their state-of-the-art entangled photon generation technology as a key component of the quantum repeater system.
The realization of quantum repeaters requires not only quantum photonic chip technologies, but also system-level operational design, application-specific integrated circuits (ASICs) for high-speed multiplexing, and ultra-low-loss packaging technologies, necessitating highly interdisciplinary research efforts. Accordingly, Professor Joonwoo Bae and Professor Wanyeong Jung from the School of Electrical Engineering, KAIST, along with Professor Donguk Nam from the Department of Mechanical Engineering, are participating as co-investigators, contributing their expertise across these domains.
This project is conducted as part of the Quantum Science and Technology Flagship Program, a national quantum initiative led by the Ministry of Science and ICT of Korea. The program will be carried out over approximately eight years through 2032, with a total budget of KRW 645.4 billion, pursuing mission-oriented research and development across three major areas: quantum computing, quantum communication, and quantum sensing. The KAIST research team has been selected for one of the five core projects in the quantum communication domain and will receive approximately KRW 12.8 billion in research funding.
If the quantum repeater is successfully realized through this research, it is expected to extend current quantum key distribution (QKD) technologies—currently limited to distances of around 100 km—to a global scale, thereby making a decisive contribution toward the realization of the quantum internet.
