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Overview
Quantum Key Distribution (QKD) is a method for establishing cryptographic keys whose security is guaranteed by the laws of physics rather than computational hardness assumptions. Unlike post-quantum cryptography (PQC), which replaces classical algorithms with quantum-resistant math, QKD physically distributes symmetric key material via quantum channels — typically fiber optic links carrying single photons or entangled photon pairs. Any eavesdropping attempt disturbs the quantum states, making interception detectable in principle.
The dominant commercial approach is entanglement-based QKD (eQKD), derived from the BBM92 protocol. A central photon source generates polarization-entangled pairs; each endpoint measures its photon, and the correlated measurement outcomes yield a shared key without transmitting the key itself. This eliminates trust assumptions around the photon source and removes the need for trusted relay nodes for inter-city distances.
QKD is complementary to PQC rather than a direct substitute. PQC secures software and protocols; QKD secures key exchange on dedicated fiber infrastructure. Governments and critical infrastructure operators with long secrecy requirements (finance, defense, telecoms backhaul) are the primary market.
Key Themes
- Entanglement-based QKD removes the “trusted relay node” requirement that limits prepare-and-measure QKD to shorter hops
- Commercial viability depends on reducing cost, size, and operational complexity of photon source and detector hardware
- European vendors (Austria, UK) lead early commercialization; China has deployed QKD at national scale (Beijing-Shanghai backbone) but as state infrastructure
- Hybrid deployments combining QKD-distributed keys with conventional AES encryption are the most practical near-term architecture
Companies
Startups & Development Partners
| Company | HQ | Stage | Mission |
|---|---|---|---|
| zerothird | Vienna, Austria | Seed+ | Entanglement-based QKD systems and Key-as-a-Service for enterprise and critical infrastructure |
| Toshiba Quantum | Cambridge, UK | Growth | QKD hardware and quantum networks, spun out of Toshiba Research Cambridge |
| ID Quantique | Geneva, Switzerland | Growth | QKD systems, quantum random number generators; one of the earliest commercial QKD vendors |