Atomic-Precision Silicon Qubits and the Path to Fault Tolerance with Michelle Simmons

Michelle Simmons is the founder and CEO of Silicon Quantum Computing (SQC) and a Scientia Professor at UNSW Sydney. She is one of the few people in the field who has simultaneously run a 200-person academic research centre, founded Australia's first vertically integrated quantum computing company, shaped how the community publishes its results (as inaugural editor-in-chief of npj Quantum Information), and influenced national quantum policy. That combination of roles gives her an unusually grounded view of what is actually hard — in the physics, in the manufacturing, and in the business.

The conversation is happening at a specific inflection point. SQC published two landmark Nature papers within ten weeks of each other in late 2025 and early 2026 — an 11-qubit silicon processor with two-qubit gate fidelities reaching 99.99%, and a 15,000-site analogue simulator demonstrating a metal-insulator transition. The company has advanced to Stage B of DARPA's Quantum Benchmarking Initiative, a program whose stated opening position is skepticism that fault-tolerant quantum computing is achievable by 2033. And SQC is now shipping an analog quantum AI chip to commercial customers. This episode is for anyone who wants to understand what silicon spin qubits actually are, why the donor-qubit approach is architecturally distinct from the CMOS-foundry approaches most competitors use, and what a credible long-range quantum roadmap looks like when it is grounded in manufacturing reality rather than theoretical aspiration.

What We Get Into

• Why qubit quality improves with scale in SQC's system — the physical intuition behind using phosphorus donor atoms as "nature's perfect qubit," and why minimizing interfaces is the key insight that separates this approach from gate-defined quantum dots
• The STM as a manufacturing tool, not just a microscope — how Simmons reframed the scanning tunneling microscope as the atomic-scale equivalent of an ASML stepper, and why 25 years of development now yields half a million registers in half a day at sub-nanometer precision
• What the 15,000-site analogue simulator actually demonstrated — the distinction between analogue simulation and gate-model computation, what a metal-insulator transition tells you about correlated quantum matter, and why this device is also a tool for validating the gate-model processor as it scales
• Six qubits per lead and all-to-all connectivity — how hyperfine frequency selection lets SQC address multiple nuclear spin qubits through a single electrical lead, and why that matters for error correction overhead
• The eight-stage roadmap, set in 2014, and how it has held up — Simmons mapped her milestones onto the 1947–1981 arc of classical semiconductor development; two of the three near-term milestones came in ahead of schedule
• DARPA QBI Stage B: what it validates and what it doesn't — why Simmons describes the program as "gold for a company" and how external scrutiny is forcing SQC to solve operating-environment questions earlier than planned
• Quantum reservoir computing as a near-term product — how SQC's analog AI chip is already in customers' hands, cutting one communications company's training time from three weeks to two days, and why this is a bridge to the fault-tolerant era rather than a detour from it
• Why you cannot outsource quantum manufacturing — Simmons's argument, drawn from decades of hands-on fabrication, that the teams who treated manufacturing as a commodity have paid a steep price
• The hype question, answered by someone who has lived it — as a journal editor, APS division chair, and company CEO, Simmons has a rare vantage point on where the field's communication problems actually originate
• What "fault tolerant" will need to mean in 2033 — and why the definition of that phrase is going to require as much parsing as the hardware milestone itself

Resources & Links

Guest & Company

• Silicon Quantum Computing (SQC) — SQC's official site; the news feed covers all major 2025–2026 milestones including the DARPA Stage B announcement and commercial partnerships
• UNSW Staff Profile — Michelle Simmons — Academic profile with full publication list and institutional roles

Papers & Results

• Nature — "Large-scale analogue quantum simulation using atom dot arrays" (2026) — The primary paper on the 15,000-site Quantum Twins analogue simulator; the result discussed in the episode
• Nature — "An 11-qubit atom processor in silicon" (Dec 2025) — The primary paper on SQC's 11-qubit processor, demonstrating high-fidelity operation across two interconnected nuclear spin registers
• HPCwire — SQC Demonstrates High-Accuracy Grover’s Algorithm Execution Without Error Correction (Feb 2025) — SQC's announcement of its Grover’s algorithm results, published in Nature Nanotechnology
• The Quantum Insider — SQC Silicon Processor Scales Without Fidelity Loss (Dec 2025) — Analysis of the 99.99% two-qubit gate fidelity result and what it means for the donor-qubit architecture
• Phys.org — Quantum Twins Simulator Unveils 15,000 Controllable Quantum Dots (Feb 2026) — Accessible summary of the analogue simulator paper for non-specialist readers

DARPA Program

• SQC — DARPA Quantum Benchmarking Initiative Stage B Announcement — SQC's official release on advancing to QBI Stage B
• DARPA — QBI Stage B Selection — Official DARPA page listing the 11 Stage B participants

Context & Analysis

• Interesting Engineering — Michelle Simmons Interview (Dec 2025) — First-person interview on silicon qubits, commercial strategy, and the 2033 roadmap; useful companion reading to this episode
• postquantum.com — Silicon Quantum Computing Company Profile (2026) — Independent commercial and technical assessment of SQC's position in the competitive landscape

Key Quotes & Insights

"Nature's perfect qubit." Simmons's phrase for the phosphorus donor atom in silicon: the qubit state forms naturally when the atom is placed, without complex materials engineering, in an environment where the silicon matrix acts as the vacuum does for trapped ions.

"Every atom counts." SQC's company motto, and a literal description of their manufacturing philosophy — because they know the position and behavior of every atom in every device, every chip is a learning opportunity.

> "I've never really seen...