Photonic quantum computing

Quantum computing that encodes qubits in single photons of light, routed through optical circuits on chips.

• Photons barely interact with their surroundings, so they hold quantum states well and travel through fibre, though detectors usually need deep cooling.
• The optical circuits can be built in existing silicon-photonics fabs; PsiQuantum works with GlobalFoundries.
• Photons also barely interact with each other, so entangling operations succeed only probabilistically and must be retried and combined at huge scale.
• Every lost photon is an error, so optical loss in each component, not gate speed, is the metric that decides feasibility.