The development of practical quantum computers remains a significant challenge despite recent advancements in hardware. While qubit counts now exceed one hundred, the limitations of current technology hinder the implementation of large-scale quantum error correction and fault-tolerant quantum computation (FTQC). This necessitates not only continued hardware improvements but also crucial software advancements, such as algorithms designed to reduce the qubit requirements for FTQC. Fujitsu, with its long history in high-performance computing, is actively addressing these challenges through a comprehensive research and development (R&D) program encompassing all layers of the quantum computing stack, from device physics to algorithms and applications. This R&D is conducted in collaboration with world-leading research institutions including RIKEN, Delft University of Technology (TU Delft), and Osaka University.

Our hardware efforts focus on two qubit technologies: superconducting qubits (in collaboration with RIKEN) and diamond-spin qubits (with TU Delft). We recently launched a 64-qubit superconducting quantum computer (October 2023) [1] and are developing 256- and 1000-qubit systems. Research focuses on improving qubit uniformity [2] and overall performance of our quantum computers. Our diamond-spin qubit technology [3] utilizes tin-vacancy (SnV) centers in diamond [4], offering flexible qubit connectivity through photonic entanglement, potentially enabling novel quantum error correction codes to reduce error correction overhead.

Our software development, in collaboration with Osaka University, concentrates on FTQC, including error correction [5, 6] and logical gate operations. We have proposed a novel "partially" fault-tolerant architecture designed to significantly reduce the qubit and gate count requirements for practical applications [7].

To accelerate application development, we offer a hybrid quantum computing platform combining our 64-qubit quantum computer and a 40-qubit simulator, leveraging Fujitsu's high-performance computing expertise. This platform supports collaborations with end-users in materials science, drug discovery, and finance, with demonstrated success in hybrid quantum-classical algorithms for quantum chemistry calculations [8]. This presentation summarizes Fujitsu's comprehensive approach to advancing quantum computing technology.

Dr Shintaro Sato is Fellow, SVP, Head of Quantum Laboratory at Fujitsu Research, Fujitsu Limited, Japan. He concurrently serves as Deputy Director of the RIKEN RQC-Fujitsu Collaboration Center. Leading research at the Quantum Laboratory, he oversees all aspects of quantum computing technology, from device and platform to software and applications. In October 2023, Fujitsu, in collaboration with RIKEN, released a 64-qubit superconducting quantum computer - a first for a Japanese company. Fujitsu and its collaborators received the Prime Minister’s Award as part of the 53rd Japan Industrial Technology Awards in 2024 for successfully developing a high-performance computing platform leveraging this 64-qubit computer. His laboratory also collaborates with TU Delft in the Netherlands on diamond-spin qubit technology. Prior to his work in quantum computing, he conducted research on post-silicon devices using carbon nanotubes and graphene, receiving several research awards, including the JSAP (the Japan Society of Applied Physics) Fellow Award in 2018. From 2010 to 2014, he led a group at the National Institute of Advanced Industrial Science and Technology, working on "green nanoelectronics" funded by the Japan Society for the Promotion of Science through the First Program. He also held a concurrent position at Semiconductor Leading-Edge Technologies, Inc. from 2006 to 2010. He joined Fujitsu after receiving his Ph.D. in Mechanical Engineering from the University of Minnesota in 2001. He earned his MS in Science and Engineering (Physics) from the University of Tsukuba in 1990. His research interests include nanomaterials, nanoelectronics, and quantum computing.

^{[1] https://www.fujitsu.com/global/about/resources/news/press-releases/2023/1005-01.htm [2] T. Takahashi, et. al., Jpn. J. Appl. Phys. 62, SC1002 (2023). [3] R. Ishihara et al.,
IEDM2021, doi: 10.1109/IEDM19574.2021.9720552. [4] M. Pasini et al., Phys. Rev. Lett. 133, 023603 (2024). [5] J. Fujisaki, et al., Phys. Rev. Research 4, 043086 (2022). [6] J. Fujisaki, et al., Phys. Rev. Research 5, 043261 (2023). [7] Y. Akashoshi, et al., PRX Quantum 5, 010337 (2024). [8] N. Iijima, et al., arXiv:2311.09634 (2023).}