Quantum computers based on several different hardware technologies have been proposed and demonstrated recently. The number of qubits for such computers now exceeds one hundred. However, practical applications of quantum computers are yet to be realized. One of the reasons for this is the existence of relatively large errors in qubit operations and readout. Another reason is that the number of qubits is insufficient for implementing large-scale quantum error correction and realizing fault-tolerant quantum computation (FTQC). In addition to hardware issues, efforts in software technology, for instance, to reduce the number of qubits required for FTQC are also important.
Fujitsu has been working on high-performance computing technologies for years. We are actively pursuing quantum computing to address societal challenges intractable for conventional computers. We are committed to research and development (R&D) across all layers of quantum computing, from quantum devices to algorithms and applications. Our R&D efforts are conducted in collaboration with world-leading research institutions, including RIKEN, Delft University of Technology (TU Delft), and Osaka University.
In hardware technologies, Fujitsu focuses on two qubit technologies: superconducting qubit technology developed with RIKEN and diamond-spin qubit technology with TU Delft. In October 2023, we launched a 64-qubit superconducting quantum computer at RIKEN RQC-Fujitsu Collaboration Center [1]. We are now developing 256- and 1000-qubit superconducting quantum computers, which will be released in the near future. In the presentation, our efforts to improve the uniformity in qubit characteristics [2] and the performance of our quantum computers will be briefly discussed.
We also work on diamond-spin qubit technology with TU Delft [3]. We use an electron spin formed at tin-vacancy (SnV) in diamond as a qubit [4]. Nuclear spins of 13C in the vicinity of SnV are also used as qubits. In this technology, since SnV qubits can be entangled with each other using photonic interconnect, there is freedom in the topology of qubit connections. So it may be possible to implement a new quantum error correction code for our diamond spin qubits, possibly reducing the overhead for error correction in the future.
Our collaboration with Osaka University focuses on software for fault-tolerant quantum computing (FTQC), including technologies for error correction [5, 6] and logical gate operations. We have recently proposed a novel quantum computing architecture that incorporates error correction [7]. This "partially" fault quantum computing approach aims to significantly reduce the number of qubits and gate operations required for practical quantum computing.
Furthermore, we are dedicated to developing practical quantum computer applications. In 2022, we launched research collaborations with end-users in the fields of materials science, drug discovery, and finance, leveraging Fujitsu's quantum computer simulator, which draws upon our expertise in high-performance computing (HPC). We now provide end-users with a hybrid quantum computing platform consisting of our 64-qubit quantum computer and 40-qubit quantum computer simulator for application development. In fact, we developed and demonstrated a hybrid algorithm both using a quantum computer and a simulator for quantum chemistry calculations [8].
This presentation will provide a concise overview of Fujitsu's comprehensive quantum computing research activities, including collaborative efforts at the RIKEN RQC-Fujitsu Collaboration Center.
[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).
Keywords: Quantum computer, Superconducting qubit, Diamond spin qubit, Error correction