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PsiQuantum's Path to 1 Million Photonic Qubits: Aspiration vs. Quantum Resistant Reality

7 min read

The Photonic Bet

PsiQuantum (Palo Alto, California, with build sites in Brisbane and Chicago) is pursuing a fault-tolerant photonic quantum computer with approximately 1 million physical qubits. If successful, this would be the largest quantum computer by any measure. PsiQuantum has received over $2 billion in combined private and public funding including a $1 billion Series E in September 2025.

Why Photonic?

Photonic quantum computing uses single photons as qubits, routed through silicon nitride waveguides. Advantages:

Room temperature operation. No millikelvin cryogenics.
Natural networking. Photons move at the speed of light and can traverse fiber.
Linear scaling. Adding chips is a matter of fiber interconnect, not exotic coherent connections.

Disadvantages:

Probabilistic gates. Photonic quantum gates are inherently probabilistic; fault tolerance requires extensive multiplexing.
Photon loss. Every waveguide, connector, and component loses some photons.
Single-photon sources. Producing true single photons at scale is hard.

PsiQuantum's approach uses "fusion-based quantum computing" with large photonic cluster states and fault-tolerant measurement-based protocols.

The Brisbane and Chicago Facilities

Brisbane, Australia: Announced April 2024. $940 million AUD combined federal and state funding. Target: utility-scale photonic quantum computer operational by end of 2027.
Chicago, Illinois: Announced 2024. State of Illinois investment announced alongside Series E.

$1 Billion Series E (September 2025)

PsiQuantum announced a $1 billion Series E funding round in September 2025, led by Blackrock and other institutional investors. This brings total funding above $2 billion and funds the Brisbane and Chicago buildouts.

The 1 Million Qubit Aspiration

PsiQuantum has communicated a target of approximately 1 million physical photonic qubits as the threshold for useful fault-tolerant quantum computing. Important caveats:

This is a company aspiration, not a peer-reviewed milestone.
Fusion-based quantum computing resource estimates require significant breakthroughs in photon detection efficiency and single-photon source purity.
Even 1 million photonic qubits may not directly break RSA-2048 depending on the logical qubit overhead.

Photonic Quantum Computing's Peer-Reviewed Base

Separate from PsiQuantum's commercial program, photonic quantum has produced real scientific results:

Jiuzhang 3.0 (USTC, October 2023): 255 detected photons in boson sampling.
Xanadu (Canada): photonic quantum systems with demonstrated advantage on specific sampling tasks.
Various academic lab demonstrations of small-scale fault-tolerant photonic protocols.

DARPA QBI Participation

PsiQuantum is one of 11 companies advanced to Stage B of DARPA's Quantum Benchmarking Initiative (November 2025). DARPA's stated goal: independently verify fault-tolerant utility-scale quantum computing by 2033.

Implications

Photonic scale-up is a real path but unproven at the thousands-of-logical-qubits regime.
Brisbane and Chicago timelines (utility-scale by 2027-2028) are company projections. Treat them as ambitious but not guaranteed.
If PsiQuantum delivers, the CRQC timeline could compress. If it does not, we remain on superconducting + trapped-ion trajectories.
For your PQC migration: deploy ML-KEM hybrid on NIST FIPS 203/204/205 today independent of PsiQuantum's trajectory.

Frequently Asked Questions

Has PsiQuantum built a million-qubit quantum computer?

Not yet. The 1 million qubit target is an aspirational company goal. Current demonstrations have far fewer photonic qubits. PsiQuantum projects utility-scale operation by 2027-2028 at Brisbane and Chicago.

What is the PsiQuantum Brisbane deal?

April 2024 announcement of $940 million AUD combined federal and Queensland state commitment to a photonic quantum computing facility in Brisbane, Australia. Target: utility-scale photonic quantum computer by end of 2027.

Is photonic quantum computing faster than superconducting?

Photon gates operate at light speed, but fusion-based quantum computing requires extensive multiplexing and error correction that imposes its own overhead. Effective gate speed depends on the total protocol, not just the photon travel time.

Could PsiQuantum break RSA?

A fully-scaled, fault-tolerant photonic quantum computer at PsiQuantum's 1-million-qubit aspiration could in principle run Shor. As of April 2026 this remains aspirational. Migrating to PQC now protects you regardless of which hardware path arrives first.

Sources

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Originally published at quantumsequrity.com/blog/psiquantum-photonic.