Superconducting Qubits, STAR Architecture, and Diamond-Spin Qubits with Dr. Shintaro Sato

Dr. Shintaro Sato is a Fellow and Head of the Quantum Laboratory at Fujitsu Research, and Deputy Director of the RIKEN RQC-Fujitsu Collaboration Centre. He oversees Fujitsu's entire quantum effort — from device fabrication through error correction architecture, software, and application research — and has been building toward commercial quantum systems since Fujitsu began its serious quantum R&D push around 2020. With over 164 publications spanning graphene nanoelectronics, superconducting qubit design, and fault-tolerant architectures, he brings both deep technical credibility and a rare full-stack perspective.

This conversation is timely because two significant developments converged almost simultaneously just before recording: Fujitsu announced a tin-vacancy (SnV) diamond-spin prototype developed with TU Delft and QuTech, and began testing its STAR error-correction architecture on neutral-atom hardware with startup Yaqumo — an explicit signal that Fujitsu is betting on hardware-agnostic software layers even as it races to scale its own superconducting devices. Listeners who follow quantum hardware roadmaps, fault-tolerant computing, or Japan's national quantum strategy will find this episode unusually specific and candid.

What We Get Into

• How Fujitsu actually fabricates its superconducting chips — Sato explains how the team adapted Nakamura-sensei's original RIKEN designs, developed their own Josephson junction uniformity techniques, and built a research fab capability from scratch rather than licensing finished devices.
• Why packaging is the hardest problem at 1,000+ qubits — not the qubits themselves, but the superconducting wiring, chip-to-chip interconnects, interposers, and the sheer number of control lines running from room temperature to millikelvin. Sato is candid that his engineers "don't want to do it anymore."
• What STAR architecture actually does — it's not a new error-correction code; it operates at the logical gate layer above the surface code, replacing the notoriously expensive T gate with phase-rotation gates and selectively reintroducing T gates only when rotation angles would otherwise accumulate too much error. Version 3 achieves roughly a 10x accuracy improvement over version 2 for the same physical qubit count.
• Why STAR is hardware-agnostic — because it operates at the logical operation layer rather than the physical error-correction layer, it can in principle run on any hardware modality. Fujitsu has now begun testing it on Yaqumo's neutral-atom platform, and Sato mentions QuEra has also demonstrated STAR independently.
• What tin-vacancy (SnV) diamond-spin qubits are actually for — not a replacement for superconducting qubits, but a photonic interconnect technology. SnV centers emit photons that can carry quantum information between modules, potentially linking separate dilution refrigerators — a transduction approach that sidesteps one of the hardest problems in scaling superconducting systems.
• The speed mismatch problem in hybrid architectures — superconducting qubits operate at gigahertz speeds; nuclear spins in diamond-spin systems operate at kilohertz. Sato acknowledges this directly and frames it as an architectural challenge analogous to CPU-memory hierarchies in classical computing.
• What Fujitsu's open-source strategy looks like in practice — the collaboration with Osaka University on Project Octopus, which produced an open-source full-stack control and software platform, is now being adopted as part of Fujitsu's commercial offering.
• What 2030 actually looks like — Sato is measured: a 10,000-qubit machine will still be a "very small scale logical quantum computer," most useful for quantum chemistry in hybrid HPC+quantum workflows. Revolutionary applications will come incrementally, not all at once.
• The long-term vision — Sato's stated dream is a quantum computer small enough to fit in a smartphone, which he acknowledges requires entirely different physics than anything on today's roadmap.

Resources & Links

Guest & Organization

• Dr. Shintaro Sato — Fujitsu Quantum Day Profile — Fujitsu's own bio page covering Sato's dual role at Fujitsu Research and RIKEN RQC-Fujitsu Collaboration Centre.
• Shintaro Sato — ResearchGate Profile — Full publication list (164 papers, 3,096 citations); useful for tracing his path from graphene nanoelectronics to quantum architecture.
• Interview with Shintaro Sato — QuTech — Sato discusses the NV-center and diamond-spin collaboration with QuTech and the vision for quantum-as-a-service.

Hardware Roadmap & STAR Architecture

• Fujitsu Quantum Day 2026 — Sato Presentation Slides (PDF) — Primary-source slides showing the full hardware roadmap: 64 → 256 → 1,024 → 10,000+ qubits with STAR architecture milestones.
• Fujitsu Officially Starts 10,000+ Qubit Development — Fujitsu Press Release (Aug 2025) — Official announcement of the early-FTQC 10,000-qubit program targeting FY2030.
• STAR Architecture Overview — Fujitsu Global — Technical explainer for STAR ver. 3 (announced March 2026), including the qubit-reduction claims for ruthenium-catalyst calculations.
• How Fujitsu Is Tackling a 10,000-Qubit Quantum Computer — The Quantum Insider (Dec 2025) — Deep-dive on STAR architecture and the 250-logical-qubit target.

Diamond-Spin & SnV Prototype

• Fujitsu Develops Diamond-Spin Quantum Computer Prototype — The Quantum Insider (Sept 2026) — Announcement of the SnV-center diamond-spin QPU prototype from the Fujitsu/TU Delft/QuTech collaboration.
• Fujitsu Diamond-Spin SnV Prototype Analysis — Quantum Computing Report (Sept 2026) — Technical breakdown of SnV center advantages, photon emission characteristics, and hybrid roadmap context.
• Fujitsu and QuTech Realize High-Precision Quantum Gates — Fujitsu Press Release (Mar 2025) — NV-center two-qubit gate fidelity result (<0.1% error) published in Physical Review Applied; the technical foundation for the SnV work discussed in this episode.

Neutral-Atom / Yaqumo Collaboration

• Fujitsu and Yaqumo Begin Testing on Neutral-Atom Hardware — The Quantum Insider (Sept 2026) — Breaking news on STAR validation on Yaqumo's neutral-atom processors, announced just before this recording.