Physics / mechanism
Quantum communications exploits quantum mechanical properties—superposition, entanglement, no-cloning theorem—to transmit information with information-theoretic security. The dominant near-term protocol is QKD (Quantum Key Distribution), specifically BB84 (polarisation-encoded photons) and its variants. Key parameters: QBER (quantum bit error rate, must stay <11% for BB84), secret key rate (SKR, currently ~Mbps over ~100 km fibre, dropping sharply beyond), and transmission distance (record ~1,000 km via satellite relay, Micius). Repeater-based long-haul requires quantum memory with coherence times >ms—still pre-commercial. Hardware stack: single-photon sources (InGaAs SPADs, SNSPDs), entanglement sources (SPDC crystals), and classical post-processing ASICs. CV-QKD (continuous variable) is an alternative gaining ground for telecom-compatible integration.
Competitive landscape
Classical encryption (AES-256, RSA) is the incumbent—cheap, fast, widely deployed, but theoretically vulnerable to cryptanalytically relevant quantum computers (CRQC). Post-quantum cryptography (PQC, NIST-standardised: ML-KEM, ML-DSA) is the direct competing approach—software-only, backward-compatible, deployable today, and structurally cheaper. QKD’s differentiation is forward secrecy against both classical and quantum adversaries and physics-based rather than computational security guarantees.
| Approach | Deployment cost | CRQC resistance | Infrastructure change |
|---|---|---|---|
| QKD | High | Yes | Major (dedicated fibre/satellite) |
| PQC | Low | Assumed | Minimal |
| Hybrid QKD+PQC | High | Strong | Major |
Companies using
Connected ideas
Sources
Frontier (open questions)
- To be added.