No random number generator you鈥檝e ever used is truly, provably random 鈥� but this one is. Researchers have used an experiment developed to test quantum mechanics to generate demonstrably random numbers, which could come in handy for encryption.
鈥淲ith standard random number generators, there鈥檚 no real way to put a certificate of randomness on it,鈥� says at the US National Institute of Standards and Technology in Boulder, Colorado. 鈥淲ith this one, it鈥檚 guaranteed to be random by the laws of physics.鈥�
In quantum mechanics, a single photon 鈥� a particle of light 鈥� can exist in a superposition of two states of polarisation, like a coin mid-flip. The coin is equally likely to land on heads or tails, but it鈥檚 impossible to know until you toss it. The same goes for the photon, which is simultaneously polarised at two different angles until it collapses into one state when it鈥檚 measured.
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This quantum rule is the foundation of the new random number generator built by Bierhorst and his colleagues.
Filtered photons
First, they use a specialised laser to produce a pair of entangled photons, each in a superposition of two different polarisations. It shoots each photon towards its own detector, each fitted with a filter that allows only photons of a particular polarisation to pass.
The detectors are 187 metres apart, and one of two possible filters for each is chosen in the last moments before the photons hit them. This is to ensure that no information can be shared between the detectors about which filters were chosen 鈥� to do so, any signal would have to travel faster than the speed of light.
Each entangled photon has a 50 per cent chance of passing through the filter, depending on which state it collapses into. A photon that makes it through the filter is measured as a 1, and a one that doesn鈥檛 is measured as a 0. These random 1s and 0s can later be strung together and converted into integers to be used in encryption or sensitive PINs.
Entanglement lasts
This setup is called a Bell鈥檚 test, and it is designed to ensure that the final polarisation state of each photon is not affected by outside forces. If the measurements of each photon at the end of the test remain similar, it proves they are still entangled and have not been tampered with, either by a part of the apparatus drifting out of place or by someone trying to intercept the signal.
鈥淚n principle, an adversary or eavesdropper could have started messing around with your particles, but if you see these crisp correlations between the particles that鈥檚 a guarantee that nothing else has influenced them or gotten in the way,鈥� says at the Massachusetts Institute of Technology.
The experiment鈥檚 success rate was low 鈥� out of 55 million photon pairs, just 1024 usable random bits were produced. That鈥檚 enough to confirm the true randomness of the output, but not enough to be put to practical use.
Nature
Read more: Starlight test shows quantum world has been weird for 600 years
