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.