Photonic quantum computing
Also known as: optical quantum computing, photonic qubits, linear optical quantum computing, light-based quantum computing
Photonic quantum computing uses photons, particles of light, as qubits.
Photons barely interact with their environment, so they hold quantum information well and travel easily through fibre, making networking natural. While those are big advantages, the same weak interaction makes it hard to get photons to interact for two-qubit gates. Companies such as Toronto's Xanadu and California's PsiQuantum are betting they can solve that at scale.
Photonic quantum computing, explained at three levels
At home
Instead of atoms or tiny circuits, photonic quantum computers use particles of light as qubits. Light can travel through fibre-optic cables, so these computers could connect to each other more easily, like a quantum internet.
At work
Photonic quantum computing could make it easier to build large systems by linking smaller modules with fibre. Some photonic approaches also avoid the extreme cooling needed for other qubits, though detectors often still require cold temperatures.
At home
Photons can encode qubits in properties such as their path, polarization, or arrival time. Because photons don't easily interact with each other, creating entanglement requires clever tricks, such as measuring some photons in a way that affects others.
At work
Photonic systems use chip-based optical circuits made in semiconductor foundries, which could help with manufacturing scale. Key challenges include photon loss (each lost photon is an error), reliable photon sources, and efficient detectors. Measurement-based approaches, which prepare large entangled states and then measure them, are common in photonics.
At home
Some photonic designs use 'continuous-variable' encodings, such as squeezed light, rather than individual photons, including special error-resistant states called GKP qubits. In my view, these approaches show how photonics researchers are rethinking what a qubit even looks like, which is part of the field's appeal.
At work
Fusion-based architectures, pursued by PsiQuantum, create small entangled resource states and 'fuse' them through measurements into larger structures for error correction. Loss tolerance thresholds are a central metric. Strategic advantages include compatibility with telecom infrastructure and foundry manufacturing, but timelines for fault-tolerant photonic systems remain uncertain.
Real-world examples
At home
Lena toured a Toronto tech showcase and learned that Xanadu was building quantum computers using light. She was surprised that a Canadian company was competing with tech giants in one of the most advanced areas of quantum research.
At work
Thomas works on research partnerships at a Canadian university. His team partnered with a photonic quantum company to explore quantum networking, using fibre links between campus labs to test distributing entanglement.
How it compares
| feature | Photonic quantum computing | Superconducting qubits |
|---|---|---|
| Qubit | Photons (light) | Superconducting circuits |
| Operating temperature | Many components at room temperature; detectors often cooled | Near absolute zero |
| Networking | Natural, through optical fibre | Requires conversion to photons |
| Main challenge | Photon loss and creating interactions | Decoherence, wiring, cooling |
| Key players | Xanadu, PsiQuantum, Quandela | Google, IBM |
Photonics trades difficult interactions for easy networking and potential manufacturing scale.
For analysts
Canada has real strength in quantum hardware, including photonics. If you're in Canadian tech or research, I'd look at partnership and talent opportunities with local quantum companies, since the ecosystem is unusually strong for a country of its size.
History & origin
In 2001, Emanuel Knill, Raymond Laflamme, and Gerard Milburn showed that quantum computing with only linear optics and photon detection was possible in principle, though very resource-intensive. Research continued for two decades. In December 2020, a team at the University of Science and Technology of China reported quantum advantage with its Jiuzhang photonic system, performing a sampling task. Xanadu, founded in Toronto in 2016, demonstrated its own advantage claim with Borealis in 2022 and unveiled Aurora, a modular networked photonic system, in January 2025. PsiQuantum raised large funding rounds to build utility-scale systems in Australia and the US. In my opinion, photonics is the highest-risk, highest-reward hardware bet in the field, and it's notable that a Canadian company is one of its leaders.