The unique properties of quantum systems such as individual photons of light allow them to be used in provably secure cryptographic key exchange. This is of great interest to organisations such as healthcare providers, governments and financial institutions. Quantum protocols can now be deployed between dedicated nodes distant up to about 600 km using existing optic fibres — enough to link, for example, a bank headquarters and a data storage warehouse. Academic prototypes are operating at very low key generation rates over satellite links.5.6
Already very difficult to break, future implementations will provide unconditional, device-independent quantum cryptography that will be unbreakable both in theory and practice. However, a number of challenges to the widespread rollout of quantum cryptography remain. Among them are cost, bandwidth and distance, integration with standard communication systems and the need to establish certification methods that are easy to apply. A crucial breakthrough will be the development of “quantum repeaters” that can securely amplify the signals to enable their transmission over thousands of kilometres, although workarounds may be possible.7
