A network of crystals for long-distance quantum communication
Quantum physic can guarantee that a message has not be intercepted before reaching its destination. Thanks to the laws of quantum physic, a particle of light – a photon – can be in two distinct states simultaneously, comparable to a coin thrown in the air, which is virtually both head and tail before reaching the ground. Like when the coin is grabbed, this superposition of states is destroyed as soon as it is read. This peculiar feature allow one to detect an evil eavesdropper when sending a message. However, this technique is so far limited to short distances. In order to extend the reach of these quantum communications, researchers from the University of Geneva (UNIGE), Switzerland, have demonstrated a novel protocol based on a crystal than can emit quantum light as well as store it for arbitrary long times. This work, to appear in Physical Review Letters, paves the way...