Japan Unveils World’s Largest-Class Superconducting Quantum Computer with 256 Qubits
Tokyo, Japan – June 21, 2025 – Researchers at Japan’s RIKEN National Research and Development Agency, in partnership with Fujitsu, have developed a superconducting quantum computer featuring 256 qubits, marking it as one of the world’s largest-class systems of its kind. The achievement, announced on June 20, 2025, represents a significant step forward in Japan’s quantum computing ambitions.
Quantum computers leverage qubits—subatomic particles that enable vastly enhanced computational capabilities compared to traditional computers. Superconducting quantum computers, a leading hardware type, are being developed globally by companies such as Google, IBM, and Rigetti. The new system, housed at the RIKEN RQC-Fujitsu Collaboration Center in Wako, Japan, surpasses Google’s 70-qubit Sycamore processor in qubit count, though it trails IBM’s 1,121-qubit Condor processor, which is not widely accessible to external users. Experts note that achieving quantum computing’s full potential may require systems with up to one million qubits, with factors like qubit quality, noise reduction, and error mitigation being critical alongside qubit quantity.
A key innovation in the RIKEN-Fujitsu system is its quadrupled qubit density. By employing high-density integration technology and an advanced thermal design, researchers fitted 256 qubits into the same casing used for a previous 64-qubit system. This was achieved through a 3D connection structure, assembling 4-qubit “unit cells” side by side and layering them in three dimensions. “Using this structure, we can scale the quantum chip without design change,” said Yoshiyasu Doi, Senior Researcher at the RIKEN RQC-Fujitsu Collaboration Center, in an interview with Euronews Next. Fujitsu highlights that this technique allows efficient qubit scaling without complex redesigns.
Operating quantum computers requires extreme cold to maintain qubit stability. The new system includes a cooling mechanism capable of reaching 20 millikelvin, near absolute zero. Doi noted that thermal management posed a significant challenge, but the team reduced amplifier power consumption by over 60%, improving heat balance for larger-scale systems. Additionally, the system features advanced high-density cabling to manage the complex input and output connections required for each qubit. Jonathan Burnett, deputy director for research at the UK’s National Quantum Computing Centre, told Euronews Next that Fujitsu’s cabling advancements set the system apart, noting that no European group has deployed a system with comparable cable density.
Japan’s progress aligns with global efforts to advance quantum computing, which promises breakthroughs in fields like cryptography, materials science, and artificial intelligence. RIKEN and Fujitsu have been collaborating since 2020 to accelerate quantum technology development, building on Japan’s strong foundation in superconducting circuit research. The global quantum race includes major players like the United States, where IBM and Google lead, and China, which has made strides in quantum communication and computing. According to a 2024 report by the Japan Science and Technology Agency, Japan aims to deploy a practical quantum computer by 2030, supported by government investments exceeding ¥100 billion ($670 million USD) in quantum research.
While the 256-qubit system is a milestone, Doi emphasized a step-by-step approach: “To solve practical problems, we have to build a one-million-qubit system.” The RIKEN-Fujitsu collaboration plans to further refine qubit quality and scaling techniques, addressing challenges like noise and error correction to move closer to practical quantum applications.
This development underscores Japan’s growing role in the global quantum computing landscape, with the RIKEN-Fujitsu system demonstrating both technological innovation and scalable design potential.
