Quantum mechanics dictates that when any of us try to measure or interact with a quantum system to learn about what it is doing, we inevitably and irreversibly disturb it. This relationship between disturbance and information gained is fundamental. It is not something that can be overcome by building better measurement devices and probes in the future – it is built into Nature. Taken into the context of communications scenarios, it simply means that where the distribution of encryption keys for securing sensitive messages is implemented with quantum light signals, anyone covertly attempting to gain information about the keys will necessarily disturb some of the light signals as they do so. Thus, Nature ensures that eavesdroppers cannot avoid being detected – in fact even if they try to use other quantum technologies to examine the light signals.

Quantum communication systems use these quantum effects to securely distribute encryption keys, which are then utilised to protect all manner of sensitive data transmissions, such as bank transactions, or health records. Given current reliance on the security of information and communications, in transit and in storage, across all aspects of daily lives (government infrastructure and civil service, financial transactions and e-commerce, defence and security, private data in e.g. human resources), specific applications for these new quantum secure systems are numerous. Candidate sectors for early adoption include finance; ICT; defence and security; and space.

Commercial success of quantum communications technologies will require investment, foresight, technical understanding and long-term commitment. But QKD – potentially in partnership with new forms of mathematical cryptography – could form the basis of all future secure communications, which will remain safe in a future, quantum-enabled world.