What it is
Quantum communication uses single particles of light, photons, to carry information in a way that physics protects. The best known application is quantum key distribution, QKD.
QKD does not send the secret message. It lets two parties, Alice and Bob, agree on a random secret key that they can then use to encrypt data.
How it works
Alice sends photons with randomly chosen polarisations and Bob measures them with randomly chosen settings. Afterwards they compare, in public, which settings they used, and keep only the bits where the settings matched.
An eavesdropper has to measure the photons and cannot do so without disturbing them. The disturbance shows up as errors when Alice and Bob compare a sample of their key, and they simply discard the key.
Try it: send a quantum key
Alice sends 64 photons to Bob. Switch the eavesdropper on and compare the error rate in the part of the key that Alice and Bob keep.
Why it matters
Future quantum computers could break much of today's public-key cryptography. QKD and post-quantum cryptography, which uses new mathematics on ordinary computers, are complementary answers.
QKD needs dedicated fibre or satellite links and trusted equipment, so it is used where very high security matters.
Europe’s position
Europe is building EuroQCI, a quantum communication infrastructure that combines fibre networks in every Member State with a satellite segment, and several national and Horizon Europe projects test QKD in real networks.
159 EU-funded projects in quantum communication, with an EU contribution of EUR 416 million (CORDIS; the pillar is suggested automatically and pending review).
On this site
Recent EU-funded projects in quantum communication
- SYMPL: SYMmetric-key cryptography in Post-quantum worLd
- PACMAN: Post-quAntum Cryptography iMplementation with emerging non-volAtile techNologies
- QModem: Developing the world’s first quantum modem
- QTOOL: Single-Photon Light Sources for Quantum Technologies
- HarmoniQCI – Harmonising Quantum Communication
Related documents
- ETSI TS 104 015 V1.1.1 Cyber Security (CYBER); Quantum-Safe Cryptography (QSC); Efficient Quantum-Safe Hybrid Key Exchanges with Hidden Access Policies
- ETSI GR QSC 001 V1.1.1 Quantum-Safe Cryptography (QSC); Quantum-safe algorithmic framework
- ETSI TR 103 965 V1.1.1 CYBER; Quantum-Safe Cryptography (QSC); Impact of Quantum Computing on Cryptographic Security Proofs
Pages of this portal
Glossary
- QKD
- Quantum key distribution: creating a shared secret key with photons.
- Polarisation
- The direction in which the light wave oscillates, used to encode bits.
- Post-quantum cryptography
- Encryption designed to resist attacks by quantum computers.
- EuroQCI
- The European Quantum Communication Infrastructure: secure quantum communication links across the EU, on the ground and via satellite.
Learn more
Further reading
- Understanding Quantum Technologies 2025 (Olivier Ezratty, 8th edition, version 8.1 of 30 October 2025, arXiv:2111.15352 (v6), doi:10.48550/arXiv.2111.15352, CC BY-NC-ND 4.0)See Part 4: Communications and sensing
- Understanding Quantum Technologies 2026 (Olivier Ezratty, 9th edition, version 9.0 of 17 October 2026 (latest edition))See Part 4: Communications and sensing
Olivier Ezratty, Understanding Quantum Technologies (CC BY-NC-ND 4.0). Links only; no text of the book is reproduced on this portal.