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arXiv:1401.5658 · Optics Express

Ultra-fast quantum randomness generation by accelerated phase diffusion in a pulsed laser diode

Carlos Abellán, Waldimar Amaya, Marc Jofre, Marcos Curty, Antonio Acín, J. Capmany, Valerio Pruneri, Morgan W. Mitchell

Published Jan 16, 2014• 168 citations
arXivHTMLPDF

Abstract

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.

DOI
10.1364/oe.22.001645

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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.
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[ANGLÈS] Random numbers are extensively used in a broad range of applications. Nevertheless, there are two main markets from a commercial point of view: (i) secure communications and (ii) stochastic simulation. According to the generation rate and quality of the random numbers required, different approaches have been used so far, most of them based on pseudo-random number generation. However, these type of generators have already started showing weakness both in the quality and the generation rate. Thus, novel techniques based on physical processes are being studied and used nowadays. In this work an ultra-fast random number generator based on quantum vacuum fluctuations is demonstrated. Not only assuring the intrinsic randomness of quantum mechanics, but also being compliant with the speed needs of current applications. Employing a DFB laser diode in gain-switched mode and interferometry, the random phase generated in spontaneous emission events is translated into random amplitudes easily measurable using off-the-shelf components, i.e. measuring a quantum phenomena in a macroscopic way. Thus, using established models of semiconductor lasers, we predict a regime of high-visibility interference and nearly complete vacuum-fluctuation-induced phase diffusion between pulses. These predictions are confirmed by measurement of pulse amplitude statistics at the exit of the interferometer.
We demonstrate robust, high-speed random number generation using interference of the steady-state emission of guaranteed random phases, obtained through gain-switching a semiconductor laser diode. Steady-state emission tolerates large temporal pulse misalignments and therefore significantly improves the interference quality. Using an 8-bit digitizer followed by a finite-impulse-response unbiasing algorithm, we achieve random number generation rates of 8 and 20 Gb/s, for laser repetition rates of 1 and 2.5 GHz, respectively, with a ±20% tolerance in the interferometer differential delay. We also report a generation rate of 80 Gb/s using partially phase-correlated short pulses. In relation to the field of quantum key distribution, our results confirm the gain-switched laser diode as a suitable light source, capable of providing phase-randomized coherent pulses at a clock rate of up to 2.5 GHz.
[ANGLÈS] Random numbers are extensively used in a broad range of applications. Nevertheless, there are two main markets from a commercial point of view: (i) secure communications and (ii) stochastic simulation. According to the generation rate and quality of the random numbers required, different approaches have been used so far, most of them based on pseudo-random number generation. However, these type of generators have already started showing weakness both in the quality and the generation rate. Thus, novel techniques based on physical processes are being studied and used nowadays. In this work an ultra-fast random number generator based on quantum vacuum fluctuations is demonstrated. Not only assuring the intrinsic randomness of quantum mechanics, but also being compliant with the speed needs of current applications. Employing a DFB laser diode in gain-switched mode and interferometry, the random phase generated in spontaneous emission events is translated into random amplitudes easily measurable using off-the-shelf components, i.e. measuring a quantum phenomena in a macroscopic way. Thus, using established models of semiconductor lasers, we predict a regime of high-visibility interference and nearly complete vacuum-fluctuation-induced phase diffusion between pulses. These predictions are confirmed by measurement of pulse amplitude statistics at the exit of the interferometer.
Gain-switching of laser diodes is a well-established technique for generating optical pulses with random phases, where the quantum randomness arises naturally from spontaneous emission. However, the maximum switching rate is limited by the time required for phase diffusion: at high repetition rates, residual photons in the cavity seed subsequent pulses, leading to phase correlations, which degrade randomness. We present a method to overcome this limitation by employing an external source of spontaneous emission in conjunction with the laser. Our results show that this approach substantially suppresses interpulse phase correlations, restoring phase randomization at repetition rates as high as 10 GHz. This technique opens new opportunities for high-rate quantum key distribution and quantum random number generation.