Introduction to Quantum Key Distribution

Keeping personal data safe and secure is one of the greatest challenges posed by the rapid development of today’s information technology. More and more sensitive private data is stored on remote computer servers, for example in the cloud, making secure access to this data a predominant concern. Securing the access relies on encryption of information sent over public networks like the internet.

Quantum Key Distribution is a novel, future-proof technology which allows the distribution of the digital keys needed for encryption and decryption with extreme security guaranteed by the laws of Quantum Physics. The secret keys are transmitted by sending single particles of light – photons – over fibre optic networks.



A single photon cannot be split into smaller particles, and also cannot be copied without altering the information that is encoded in it. The latter is prohibited by the so called “No-Cloning Theorem” which is a direct consequence of the laws of Quantum Physics. An eavesdropper therefore has no means to get hold of the transmitted secret key without introducing a disturbance which can be detected by the communicating parties, and allows them to take countermeasures. By using a procedure called “Privacy Amplification” they can make sure that all information potentially known to the eavesdropper is removed from the secret key.

Communicating with single photons poses severe technical challenges which have to be met with innovative new technologies. Most crucially, the very weak light signal sent over optical fibre networks has to be detected with high efficiency and all optical elements in the path of the photons have to be optimised for low-loss performance. Toshiba is at the forefront in developing these new technologies and has demonstrated a range of world-record results, for example the world-highest bit rate ever transmitted with a Quantum Key Distribution system.