  We demonstrate a 6 Gbps real-time optical quantum random number generator by
measuring vacuum fluctuation. To address the common problem that speed gap
exists between fast randomness generation and slow randomness extraction in
most high-speed real-time quantum random number generator systems, we present
an optimized extraction algorithm based on parallel implementation of Toeplitz
hashing to reduce the influence of classical noise due to the imperfection of
devices. Notably, the real-time rate of randomness extraction we have achieved
reaches the highest speed of 12 Gbps by occupying less computing resources and
the algorithm has the ability to support hundreds of Gbps randomness
extraction. By assuming that the eavesdropper with complete knowledge of the
classical noise, our generator has a randomness generation speed of 6.83 Gbps
and this supports the generation of 6 Gbps information-theoretically provable
quantum random numbers, which are output in real-time through peripheral
component interconnect express interface.
