The Photonic Approach to Quantum Computing
Most public attention to quantum computing focuses on superconducting qubit systems from IBM, Google, and others. These systems use artificial atoms made from superconducting circuits, cooled to millikelvin temperatures inside dilution refrigerators. They are impressive engineering achievements, but they have an inherent limitation: they require extreme cooling infrastructure that is expensive, physically large, and difficult to scale to millions of qubits.
Photonic quantum computing takes a fundamentally different approach. It encodes quantum information in photons — particles of light — rather than in the state of a physical qubit. Photons travel through optical circuits, interact at beam splitters and phase shifters, and can be manipulated using components compatible with standard silicon chip manufacturing.
PsiQuantum, founded in 2016 and headquartered in Palo Alto, has been building toward a photonic quantum computer that can be fabricated using GlobalFoundries' commercial CMOS processes. On October 28, 2026, the company announced a significant milestone in this effort: an 8x8 optical circuit switch implemented on its silicon photonics platform.
What the 8x8 Switch Demonstrates
An optical circuit switch routes optical signals between input and output ports. An 8x8 switch can connect any of 8 inputs to any of 8 outputs, with low optical loss and fast reconfiguration time. In PsiQuantum's architecture, these switches are used to route photons between different parts of the quantum processor and to implement the measurement-based quantum operations that their architecture relies on.
The significance of the October 2026 demonstration is not the switch itself — optical switches are well-understood in classical telecommunications. The significance is that this switch was built on PsiQuantum's silicon photonics platform using processes compatible with high-volume semiconductor manufacturing. This matters because:
- Yield: Semiconductor fabs can produce millions of components per wafer. If quantum optical components can be made with the same yield characteristics as classical silicon components, the manufacturing cost per qubit drops by orders of magnitude.
- Integration density: Standard CMOS processes support feature sizes below 10 nanometers. Photonic components on this platform can be packed tightly, supporting the kind of integration density needed for millions of photonic qubits.
- Room-temperature operation: Unlike superconducting qubits, the photonic routing components operate at room temperature. Cooling is only required for single-photon detectors and certain other components, not the entire optical circuit.
How Silicon Photonics Differs from Superconducting Approaches
The architectural differences between photonic and superconducting quantum computers run deep:
| Property | Superconducting (IBM, Google) | Photonic (PsiQuantum) |
|---|---|---|
| Operating temperature | ~15 millikelvin | Room temperature (detectors near 4K) |
| Qubit lifetime (coherence) | ~100-500 microseconds | Photon loss per component (~0.1 dB) |
| Manufacturing process | Custom fab, low volume | CMOS-compatible, high volume |
| Gate type | Microwave pulses | Linear optical elements + measurement |
| Inter-chip networking | Cryogenic microwave couplers | Standard optical fiber |
| Primary scaling challenge | Cryogenic infrastructure | Photon loss and single-photon sources |
Neither architecture has yet demonstrated fault-tolerant computation at useful scale. Both have distinct engineering challenges. The superconducting approach has more mature gate fidelities but faces cooling infrastructure limits. The photonic approach has clearer manufacturing scalability but must solve photon loss at large circuit depths.
The Challenge PsiQuantum Must Solve
Every optical component introduces some loss — photons are absorbed or scattered by imperfections in the material. In classical fiber optic communications, amplifiers along the cable compensate for this loss. In quantum computing, amplifying a quantum signal would destroy the quantum information it carries. There is no quantum amplifier analogous to a classical optical repeater.
PsiQuantum's architecture addresses this through a measurement-based approach: rather than routing single photons through long circuit paths, the computation is driven by measuring many photons and using the measurement outcomes to steer the computation. This is technically valid but requires high rates of photon generation and detection to compensate for loss.
The October 2026 8x8 switch demonstration shows that the routing components can be built at the required quality on a CMOS platform. The remaining challenge is integrating high-efficiency single-photon sources and detectors at the same scale.
Multiple Competing Architectures and Blockchain Security
The simultaneous progress of superconducting (IBM), photonic (PsiQuantum), and neutral-atom (QuEra) quantum computing approaches changes the risk calculus for blockchain security in an important way.
If quantum computing depended on a single architecture succeeding, the threat timeline would depend entirely on that architecture's specific engineering challenges. With three or more credible approaches making parallel progress, the probability that at least one reaches fault-tolerant scale within a given time window is substantially higher than any individual probability.
A blockchain whose security depends on "quantum computers are still decades away" needs that claim to hold for every credible hardware approach simultaneously. The October 2026 milestones from IBM (modular couplers), PsiQuantum (silicon photonics switch), and ongoing progress from QuEra and Google suggest that assumption is increasingly difficult to defend.
PsiQuantum's Target Timeline
PsiQuantum has stated publicly that its target is to build a fault-tolerant quantum computer capable of running commercially useful algorithms in the early 2030s. The company's approach is to skip intermediate-scale noisy quantum computers entirely, focusing resources on the manufacturing infrastructure needed for fault-tolerant operation at scale.
The October 2026 silicon photonics switch is a milestone on that path. The next published milestones involve demonstrating single-photon sources and detectors integrated on the same platform, and eventually demonstrating a logical qubit maintained through photonic error correction.
For blockchain operators, the photonic path represents a threat vector that does not depend on dilution refrigerator infrastructure scaling. A CMOS-manufactured photonic quantum computer could potentially be deployed in standard data center environments, dramatically lowering the infrastructure barrier to operating cryptographically relevant quantum systems.
