One of the most applied quantum technologies is quantum key distribution, QKD - this is well known as quantum cryptography. Based on physical properties quantum states may be transported from a sender side to a receiver side without the option to secretly intercept this interconnection.

Naturally, it is evident if someone establishes a quantum connection between two stations, one should also directly research on all the ways to 'hack' such a connection. Our group has successfully established quite some quantum hacking in the past. Presently, we are researching together with commercial partners to make quantum cryptography as secure as possible.

One crucial requirement for QKD is that the preparation and the detection of the quantum states is fully random. This means that the selected states should be equally distributed, and moreover that no memory exists which carries information from one measurement to any subsequent measurement.

A number of protocols have been suggested to characterize quantum randomness - we are researching on more ways to prove to a human user of such an entropy source that the random output is truly random and not predetermined. Ideally trust into such a device can be shifted to direct human experience of the quantumness of such states.