Phys. Rev. X 4, 031056 (2014)

Random numbers form the basis of certain cryptography protocols. Yet generating a truly random sequence of numbers is not easy. Computer algorithms can produce numbers that are seemingly random, but such pseudo-random numbers are ultimately predictable and hence hackable. Genuine randomness can be found in nature, though: many light sources release photons at random time intervals.

Bruno Sanguinetti and colleagues have now shown that present-day commercial digital cameras and smartphones are sufficiently sensitive to detect streams of photons for conversion into random number sequences. The authors performed experiments with a light-emitting diode coupled to either a type of CCD detector used by astronomers or a smartphone camera. The numbers obtained from the two experiments passed a range of randomness tests — notably, the sequences had vanishing autocorrelations, indicating that they don't exhibit repetitive patterns.

As photon generation in a light-emitting diode is a quantum effect, Sanguinetti et al. call their scheme quantum random number generation. They estimate feasible random bit rates of one megabit per second — enough for basic cryptography tools. Expect a quantum random number generator app soon.