A post-processing-free single-photon random number generator with ultra-low latency

The low-latency requirements of a loophole-free Bell test prohibit time-consuming post-processing steps that arc often used to improve the statistical quality of a physical random number generator (RNG). Here we demonstrate a post-processing-free RNG that produces a random bit within 2.4(2) ns of an input trigger. We use the Allan variance as a tool for characterizing non-idealities in the RNG and designing a feedback mechanism to account for and correct long-term drift. The impact of the feedback on the predictability of the output is less than 6.4 x 10(7), and results in a system capable of 24 hour operation with output that is statistically indistinguishable from a balanced Bernoulli process.