Building the world's first million-qubit, fault-tolerant quantum computer — with photons
HQ: Palo Alto, CA, United States | Founded: 2016 | Employees: ~500 (est.) | Stage: Late Stage VC ($7B valuation, Sept 2025) | Website: https://www.psiquantum.com
PsiQuantum was co-founded in 2016 by professors and researchers Jeremy O'Brien, Terry Rudolph, Pete Shadbolt, and Mark Thompson — leaders in photonic quantum computing spun out of Bristol and Imperial College London. Before PsiQuantum, O'Brien and Shadbolt put the first quantum processor on the cloud. The founding insight: quantum computers only become commercially useful when they are fault-tolerant and million-qubit scale, and the only way to get there is to build them like semiconductors — in a fab, not a lab.
PsiQuantum's approach uses single photons as qubits, manipulated on silicon photonic chips manufactured at GlobalFoundries on standard 300mm wafers. Photons don't need dilution refrigerators at millikelvin temperatures for the compute itself and don't suffer the same error mechanisms as matter qubits — but the architecture requires extraordinary photon sources, detectors, and low-loss components, plus massive photonic interconnect. The company claims its chips are the most complex ever manufactured, and its fusion-based fault-tolerance scheme (with networked photonic links) is designed for scale from day one.
The business model is deeply industrial: PsiQuantum is building utility-scale, fault-tolerant systems anchored by government and utility partnerships — a site in Brisbane, Australia (with the Queensland and Australian governments), and a site in Chicago (the Illinois Quantum and Microelectronics Park). In September 2025 it raised a $1B Series E at a $7B valuation led by BlackRock with Temasek, Baillie Gifford, and NVIDIA participating, and has since signed a $125M contract with DARPA. Its stated target: the world's first commercially useful fault-tolerant quantum computer.
PsiQuantum is the most explicitly industrial bet in quantum computing: skip the NISQ era entirely and go straight to a million-qubit, fault-tolerant machine by manufacturing photonic chips in a commercial semiconductor fab. Its $1B Series E at $7B (September 2025) — the largest private quantum round ever at the time — funds two utility-scale sites (Brisbane and Chicago) with government partners, plus a new $125M DARPA contract. The bull case: silicon photonics is the only modality that scales with existing manufacturing, and PsiQuantum's GlobalFoundries partnership turns quantum from lab physics into a fab problem. The bear case: photonic fault tolerance demands extraordinary component performance (sources, detectors, loss), and 2027-2028 delivery timelines have historically slipped across the entire industry.
Category: Quantum Computing Startups
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