  Random numbers are essential for our modern information based society e.g. in
cryptography. Unlike frequently used pseudo-random generators, physical random
number generators do not depend on complex algorithms but rather on a physical
process to provide true randomness. Quantum random number generators (QRNG) do
rely on a process, which can be described by a probabilistic theory only, even
in principle. Here we present a conceptually simple implementation, which
offers a 100% efficiency of producing a random bit upon a request and
simultaneously exhibits an ultra low latency. A careful technical and
statistical analysis demonstrates its robustness against imperfections of the
actual implemented technology and enables to quickly estimate randomness of
very long sequences. Generated random numbers pass standard statistical tests
without any post-processing. The setup described, as well as the theory
presented here, demonstrate the maturity and overall understanding of the
technology.
