Physics / mechanism
QKD encodes cryptographic keys onto individual photons using quantum states—typically polarisation or phase. Measurement by an eavesdropper collapses the quantum state, introducing detectable bit-error anomalies (QBER threshold typically <11% for BB84). Key protocols: BB84 (polarisation), E91 (entanglement), CV-QKD (continuous-variable quadratures). Current SOTA: trusted-node fibre networks at ~400 km (TOSHIBA, ID Quantique), satellite QKD demonstrated by China’s Micius at >1,000 km. Practical key rates: ~10 kbps at 100 km over SMF. Twin-field QKD pushing repeater-less range toward 600 km. No quantum memory yet; metropolitan deployments are the commercial reality today.
Competitive landscape
Post-quantum cryptography (PQC)—NIST-standardised lattice algorithms (CRYSTALS-Kyber, Dilithium)—is the primary competitor. PQC is software-only, zero infrastructure cost, deployable now. QKD wins on information-theoretic security (no computational assumption) but loses on cost and scalability.
Companies using
Connected ideas
Sources
Frontier (open questions)
- To be added.