  A quantum random number generator (QRNG) based on gated single photon
detection of an InGaAs photodiode at GHz frequency is demonstrated. Owing to
the extremely long coherence time of each photon, each photons' wavefuntion
extends over many gating cycles of the photodiode. The collapse of the photon
wavefunction on random gating cycles as well as photon random arrival time
detection events are used to generate sequences of random bits at a rate of
4.01 megabits/s. Importantly, the random outputs are intrinsically bias-free
and require no post-processing procedure to pass random number statistical
tests, making this QRNG an extremely simple device.
