Physics / mechanism
Photonic quantum computing encodes qubits in photons—typically via polarisation, path, or time-bin degrees of freedom. Linear optical quantum computing (LOQC) uses beam splitters, phase shifters, and single-photon detectors to perform gate operations; measurement-based variants (MBQC) pre-entangle photons into cluster states then consume them through adaptive measurements. Key parameters: photon indistinguishability (>99% demonstrated in InGaAs QDs), two-photon interference visibility, detector efficiency (SNSPDs >98%), and loss per component (<0.1 dB on-chip is target). PsiQuantum targets silicon photonics fabs at scale; Quix Quantum ships 20+ mode processors; Xanadu’s Borealis demonstrated 216-mode Gaussian boson sampling. Error correction overhead remains the critical bottleneck—photon loss is the dominant error channel.
Competitive landscape
Competing modalities: superconducting qubits (IBM, Google) lead on gate fidelity and speed but require dilution refrigeration; trapped ions (IonQ, Quantinuum) offer best coherence but low clock rates; neutral atoms (Atom Computing, QuEra) scale spatially but face control complexity. Photonic competes primarily on room-temperature operation, telecom-wavelength networking, and fabrication in standard CMOS/silicon-photonics fabs.
| Approach | Operating temp | Integration path | Key weakness |
|---|---|---|---|
| Photonic | Room temp (detectors ~4K) | Si-photonics foundry | Photon loss, non-determinism |
| Superconducting | ~15 mK | Custom fab | Cryogenic infrastructure |
| Trapped ion | Room temp | Hybrid MEMS | Clock rate, shuttling overhead |
Companies using
Connected ideas
Sources
Frontier (open questions)
- To be added.