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EPJ Web of Conferences

Phase synchronization dynamics of a mutually coupled laser system for quantum random number generation

Berta Martínez-Pàmias, Miquel Rudé, Cristina Masoller

Published Jan 1, 2025• 0 citations
Publisher

Abstract

We performed an experimental and numerical study of an Indium Phosphide photonic integrated circuit designed for quantum random number generation. We investigated the dynamics of two weakly mutually coupled semiconductor lasers and the transient evolution towards the synchronization of the lasers’ optical phases. The simulated dynamics with the experimentally adjusted parameters were found to be in qualitatively good agreement with the experimental time traces. The results provide a better understanding of the evolution towards synchronization and a foundation for the optimization of the photonic quantum random number generation system.

DOI
10.1051/epjconf/202533506008

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We performed an experimental and numerical study of an Indium Phosphide photonic integrated circuit designed for quantum random number generation. We investigated the dynamics of two weakly mutually coupled semiconductor lasers and the transient evolution towards the synchronization of the lasers’ optical phases. The simulated dynamics with the experimentally adjusted parameters were found to be in qualitatively good agreement with the experimental time traces. The results provide a better understanding of the evolution towards synchronization and a foundation for the optimization of the photonic quantum random number generation system.
We performed an experimental and numerical study of an Indium Phosphide photonic integrated circuit designed for quantum random number generation. We investigated the dynamics of two weakly mutually coupled semiconductor lasers and the transient evolution towards the synchronization of the lasers’ optical phases. The simulated dynamics with the experimentally adjusted parameters were found to be in qualitatively good agreement with the experimental time traces. The results provide a better understanding of the evolution towards synchronization and a foundation for the optimization of the photonic quantum random number generation system.
We performed an experimental and numerical study of an Indium Phosphide (InP) photonic integrated circuit (PIC) designed for quantum random number generation. We studied the dynamics of two weakly mutually coupled semiconductor lasers, and the transient evolution towards the synchronization of the lasers’ optical phases. By carefully adjusting the parameters of a rate-equation model, the simulated dynamics was found to be in qualitatively good agreement with the experimentally observed time traces. Our results allow us to better understand the transient evolution towards synchronization, and provide a foundation for the optimization of the system for photonic quantum random number generation.
We present an experimental and numerical study of the probability distribution of interference pulses from two InP lasers in a photonic integrated circuit (PIC) operated in gain-switching mode through a square-wave signal that turns them on and off. Without laser coupling, the lasers’ phases are random due to quantum spontaneous emission noise, and their phase difference can be translated into a random intensity and exploited for quantum random number generation (QRNG). We analyze the coupling dynamics that lead to optical phase synchronization. Through a direct comparison between experiments and simulations, we demonstrate a clear correlation between laser coupling and the degradation of the randomness of the lasers’ optical phases, providing a better understanding of the operation and performance of the QRNG device.
Quantum random number generators, at the core of digital trust infrastructures, rely on quantum entropy sources (QESs) to produce randomness from physical processes. The quantum origin certification of a QES requires a physical model compatible with the measured signal of the device. Here, we study Quside Technologies' phase-diffusion QES consisting of a photonic integrated circuit (PIC) that uses the interference of two indium phosphide (InP) lasers operated in gain-switching by simultaneously modulating their pump currents from below to above the threshold. This produces intensity pulses in each laser that have random optical phases due to quantum spontaneous emission. The lasers' intensities interfere via heterodyning, and from the interference signal a random bit is obtained per modulation cycle. While this system offers high scalability and compactness, residual coupling between the two lasers can induce phase synchronization, thus reducing its extractable entropy. Through experiments and simulations of a physical model based on coupled stochastic rate equations, we quantify this effect and link laser coupling to phase synchronization. We further derive an analytical model for the probability distribution of the measured interference intensity, enabling direct extraction of the quantum phase difference distribution and laying the groundwork for the QES optimization.
The quantum random number generation based on laser phase noise, which is featured with high random number generation rate and ease for photonic integration, has been extensively investigated and demonstrated. Despite these advancements, a theoretical model to achieve optimal performance in terms of maximizing the random number generation rate is still incomplete. In this work, a comprehensive physical model for this scheme is introduced to accurately predict the power spectrum of entropy source and probability distribution of raw data, based on which the entropy source bandwidth and extractable randomness can be accordingly estimated and thus the system performance can be quantitatively evaluated and optimized. The model is sufficiently validated through both simulation and experiment with significant agreement under various typical setups. Furthermore, our proposal enables the proactive design of experimental parameters to achieve optimal system performance, which is crucial for the design and practical implementation of photonics integrated quantum random number generations.