  Quantum random number generators (QRNG) are based on the naturally random
measurement results performed on individual quantum systems. Here, we
demonstrate a branching-path photonic QRNG implemented with a Sagnac
interferometer with a tunable splitting ratio. The fine-tuning of the splitting
ratio allows us to maximize the entropy of the generated sequence of random
numbers and effectively compensate for tolerances in the components. By
producing single-photons from attenuated telecom laser pulses, and employing
commercially-available components we are able to generate a sequence of more
than 2 gigabytes of random numbers with an average entropy of 7.99 bits/byte
directly from the raw measured data. Furthermore, our sequence passes
randomness tests from both the NIST and Dieharder statistical test suites, thus
certifying its randomness. Our scheme shows an alternative design of QRNGs
based on the dynamic adjustment of the uniformity of the produced random
sequence, which is relevant for the construction of modern generators that rely
on independent real-time testing of its performance.
