GCRI · Quantum Technologies
Quantum communications
Quantum communications use quantum states of light to distribute encryption keys with security rooted in physics, and in future to link quantum computers and sensors in networks. Quantum key distribution works over limited distances and needs dedicated hardware and trusted nodes today. This page sets out how quantum communications work, what they can and cannot secure, and what evidence serves the network operators and security agencies weighing them.
Quantum communications in seven parts.
- 01The questionQuantum communications: how the risk develops
- 02Across the domainsQuantum communication touches the networks domains depend on
- 03IndicatorsWhat is measured, and how well
- 04SourcesWhere the evidence comes from
- 05DecisionsWho decides, and what the evidence serves
- 06Core questionsWhat experts ask
- 07MechanismsMechanisms and drivers
Quantum communications: how the risk develops.
Communications research and deployment limits. The dossier below sets out how the risk develops, what is measured, where the data come from, how it is modelled and who decides.
Measurement reveals eavesdropping
In quantum key distribution, measuring a quantum state disturbs it, so an eavesdropper introduces detectable errors. Keys are kept only when error rates are low.
Distance is limited by loss
Photons are lost in fibre, limiting direct links. Longer networks use trusted relay nodes or satellites, each with security implications.
Implementations can be attacked
Real devices deviate from ideal theory. Side-channel attacks on detectors and sources have been demonstrated, so security depends on implementation and certification.
Quantum networks are early
Distributing entanglement between distant nodes needs quantum repeaters and memories, which are still in research.
Post-quantum migration tracker.
The screen a team would use to follow this subject: its measures, states and decisions. Names are examples and values are illustrative.
Post-quantum migration tracker
Quantum communications · Crypto inventory · Wave 2
Migration
- Inventoryall crypto
- Prioritisedata lifetime
- Selectstandard algorithms
- Hybrid deployclassical and PQC
- Testinterop
- Cut overretire
Systems by priority
| Archive signing | RSA-2048 | 28 | ML-DSA hybrid | Piloting |
| VPN gateway | ECDH | 9 | ML-KEM hybrid | Planned |
| Payments HSM | RSA-3072 | 11 | Vendor roadmap | Blocked |
| Web TLS | ECDHE | 2 | Hybrid key exchange | Done |
Progress
Quantum communication touches the networks domains depend on.
- EnergyCouplingGrid control networks are candidate users of quantum key distribution.What to watchCost and range limits
- HealthCouplingHealth networks weigh QKD against post-quantum cryptography.What to watchAgency guidance on QKD use
- WaterCouplingUtilities are more likely to migrate to post-quantum algorithms.What to watchAlgorithm migration plans
Communication studies are designed for the Exponential Technology series. Standards work sits in ETSI’s QKD group and the ITU-T Y.3800 series; several national security agencies prefer post-quantum cryptography to QKD for most uses.
- Network trial reports.
- Security analyses of QKD implementations.
How quantum communications is modelled, measured and tested.
The model, its assumptions, its data and its uncertainty, in the form a scientist or engineer would check. Structures follow published methods. The values drawn are illustrative, not findings.
System model
The couplings between the systems in quantum communications: signs of influence, a reinforcing and a balancing loop, and cross-links where stress jumps.
What is measured, and how well.
Each indicator carries its unit, its cadence, the kind of source behind it and the evidence label a value would carry. No values are shown: a programme supplies them under its own authority.
| Indicator | Unit | Cadence | Source type | Label |
|---|---|---|---|---|
| QKD link distance | kilometres | per demonstration | Published experiments | REPORTED |
| Secret key rate | bits per second at a stated distance | per demonstration | Published experiments | REPORTED |
| Deployed QKD network nodes | count | annual | Operator and government reports | REPORTED |
| Security evaluations completed for QKD products | count | annual | Evaluation scheme records | Published statistics |
| Quantum memory storage time | milliseconds | per experiment | Peer-reviewed results | OBSERVED |
| Satellite QKD demonstrations | count | annual | Agency reports | REPORTED |
Where the evidence comes from.
Named public datasets and institutional records, each with its licence class. Sources by agreement are used only under their terms and never republished.
| Source | What it gives | Licence class |
|---|---|---|
| ETSI ISG QKD specifications | Component, interface and security specifications | Public, ETSI terms |
| ITU-T Y.3800 series | Network recommendations for QKD | Public, ITU terms |
| National cyber agency positions on QKD | Agency views on QKD versus post-quantum cryptography | Public, terms per agency |
| EuroQCI programme documentation | European quantum communication infrastructure plans | Public, EU terms |
| Peer-reviewed quantum communication literature | Experimental results | Licence per article |
Who decides, and what the evidence serves.
Quantum Technologies prepares evidence. The decisions below are taken by the authorities named, under their own rules, and never by the platform.
| Who decides | The question | Evidence this page serves |
|---|---|---|
| Network operators | Whether QKD fits any of their links and threat models | Use comparisons; architecture reviews |
| National cyber agencies | What position to take on QKD for government use | Implementation security evidence |
| Research funders | How to fund quantum network research | Progress on memories and repeaters |
Outputs this topic produces
- Comparisons of QKD and post-quantum cryptography for specific uses
- Network architecture reviews including trusted nodes
- Summaries of implementation security evidence
- Evidence notes for operators
What experts ask.
Communications questions weigh physical security against practical limits.
- What security does quantum key distribution actually provide, and under what assumptions?
- How far can quantum signals travel through fibre or free space before they are lost?
- Do trusted relay nodes undermine end-to-end security?
- How do implementation flaws in real devices open side channels?
- How does quantum key distribution compare with post-quantum cryptography for a given use?
Mechanisms and drivers.
Quantum key distribution relies on the principle that measuring a quantum state disturbs it, so two parties can detect an eavesdropper and agree a secret key. The security of the ideal protocol rests on physics rather than on assumptions about computational difficulty. Real systems, however, use imperfect sources and detectors, and several attacks have exploited those imperfections.
Photons are absorbed and scattered in fibre, which limits direct links to relatively short distances. Longer networks currently rely on trusted nodes, where the key is held in classical form and must be protected conventionally. Quantum repeaters, which would extend range without trusted nodes, remain a research goal. Satellites have been used to demonstrate links over long distances.
How it is studied, and where the methods stop.
| Method or data | What it shows | Limits |
|---|---|---|
| Security proofs | Theoretical security of protocols | Proofs assume idealised devices |
| Implementation testing and quantum hacking research | Vulnerabilities in real equipment | Testing cannot prove the absence of flaws |
| Network trials | Performance, key rates and operations | Trials are limited in scale and duration |
| Comparative security assessment | When quantum or post-quantum approaches fit | Depends on threat model and system constraints |
How it is studied, and what the methods cannot say.
- 01Quantum computing, sensing and communicationComparable benchmarking · Technology readiness assessment · Security implications trackingApplied here
- 02Physics and quantum scienceCharacterising qubit noise · Metrology of quantum clocks · Verifying quantum effectsApplied here
- 03Cybersecurity and cryptographyCryptographic inventory · Migration prioritisation · QKD implementation reviewApplied here
Where this page’s references lead.
The bodies and documents this page is read against. Status and editions change; each link goes to the issuing body.
Questions and answers.
What is quantum key distribution?
Is QKD unbreakable?
Should organisations use QKD or post-quantum cryptography?
Is quantum key distribution unbreakable?
Does quantum communication replace post-quantum cryptography?
What is a quantum internet?
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