https://www.sciencedaily.com/releases/2018/07/180716114602.htm

The team have developed a way of generating very rapid single-photon light pulses. Each photon, or particle of light, represents a bit of binary code -- the fundamental language of computing. These photons cannot be intercepted without disturbing them in a way that would alert the sender that something was amiss.

Transferring data using light passed along fibre optic cables has become increasingly common over the past decades, but each pulse currently contains millions of photons. That means that, in principle, a portion of these could be intercepted without detection.