Physics / mechanism
Photonic quantum computing encodes qubits in optical modes — typically via photon polarisation, path, time-bin, or squeezed-light (continuous-variable) degrees of freedom. Gates are implemented through linear-optical networks (beam splitters, phase shifters) plus photon-number-resolving (PNR) detectors; non-determinism is the core liability, addressed by measurement-based / fusion-based architectures (PsiQuantum, Xanadu). Key parameters: photon indistinguishability (>99% demonstrated in III-V QDs), two-photon interference visibility, detector efficiency (SNSPDs now >95%), and loss per component (<0.1 dB/cm in Si₃N₄). Room-temperature operation and CMOS-fab compatibility are structural advantages over superconducting and trapped-ion rivals.
Competitive landscape
Superconducting qubits (IBM, Google) dominate near-term gate fidelity (99.9% two-qubit) but require dilution refrigeration. Trapped ions (IonQ, Quantinuum) offer long coherence but slow gate rates (~kHz). Neutral atoms (QuEra, Atom Computing) scale in 2D arrays but remain early-stage. Photonics competes on interconnect-native architecture and ambient operation; it loses on deterministic entanglement generation.
Companies using
Connected ideas
Sources
Frontier (open questions)
- To be added.