We demonstrate a high bit-rate quantum random number generator by interferometric detection of phase diffusion in a gain-switched DFB laser diode. Gain switching at few-GHz frequencies produces a train of bright pulses with nearly equal amplitudes and random phases. An unbalanced Mach-Zehnder interferometer is used to interfere subsequent pulses and thereby generate strong random-amplitude pulses, which are detected and digitized to produce a high-rate random bit string. Using established models of semiconductor laser field dynamics, we predict a regime of high visibility interference and nearly complete vacuum-fluctuation-induced phase diffusion between pulses. These are confirmed by measurement of pulse power statistics at the output of the interferometer. Using a 5.825 GHz excitation rate and 14-bit digitization, we observe 43 Gbps quantum randomness generation.
@article{arxiv.1401.5658,
title = {Ultra-fast quantum randomness generation by accelerated phase diffusion in a pulsed laser diode},
author = {C. Abellan and W. Amaya and M. Jofre and M. Curty and A. Acin and J. Capmany and V. Pruneri and M. W. Mitchell},
journal= {arXiv preprint arXiv:1401.5658},
year = {2015}
}