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IEEE Photonics Technology Letters

Spatially Multiplexed Quantum Entropy Source With Single LD for 100-Gbps Random Numbers and Beyond

Ken Tanizawa, Kentaro Kato, Fumio Futami

Published Jan 11, 2023• 9 citations
Publisher

Abstract

Fast quantum random number (RN) generation is an essential technology for cryptographic applications requiring unpredictable RNs. This letter reports a spatially multiplexed quantum entropy source (QES) with a single laser diode (LD), utilizing parallel homodyne measurement of vacuum fluctuation, for an aggregated RN generation rate of 100 Gbit/s and beyond. The QES uses a high-power distributed feedback LD and a low-loss 1$\times $16 silica planar lightwave circuit splitter and achieves eight-channel parallel operation with a broad bandwidth of 4 GHz each. A four-channel aggregated RN generation rate of 4$\times $25 Gbit/s and further scalability up to$8\times25$Gbit/s with eight channels are demonstrated via offline post-processing.

DOI
10.1109/lpt.2023.3234260

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Fast quantum random number (RN) generation is an essential technology for cryptographic applications requiring unpredictable RNs. This letter reports a spatially multiplexed quantum entropy source (QES) with a single laser diode (LD), utilizing parallel homodyne measurement of vacuum fluctuation, for an aggregated RN generation rate of 100 Gbit/s and beyond. The QES uses a high-power distributed feedback LD and a low-loss 1×\times ×16 silica planar lightwave circuit splitter and achieves eight-channel parallel operation with a broad bandwidth of 4 GHz each. A four-channel aggregated RN generation rate of 4×\times ×25 Gbit/s and further scalability up to8×258\times258×25Gbit/s with eight channels are demonstrated via offline post-processing.
Unpredictable random number (RN) generation is an essential technology for cryptographic applications. Quantum RN generators (QRNGs) have attracted significant attention owing to their generation of RNs utilizing the randomness guaranteed by quantum mechanics. Vacuum fluctuations are a promising entropy source of quantum randomness. These are detected using a homodyne setup with a laser source and a beam splitter. QRNGs based on vacuum fluctuations can generate RNs at a high-speed and in a stable manner. This paper reports a high-speed spatially multiplexed QRNG based on vacuum fluctuations using a single semiconductor laser diode and an integrated optical beam splitter. The QRNG obtained four independent vacuum fluctuations across a wide bandwidth of over 2 GHz. The RNs were extracted in parallel using a field-programmable gate array with analog-to-digital converters. An aggregated real-time RN generation rate of 4×12.5 Gbit/s was achieved. The generated RNs passed a randomness test based on NIST SP800-90B.
Fast secure random number generation is essential for high-speed encrypted communication, and is the backbone of information security. Generation of truly random numbers depends on the intrinsic randomness of the process used and is usually limited by electronic bandwidth and signal processing data rates. Here we use a multiplexing scheme to create a fast quantum random number generator structurally tailored to encryption for distributed computing, and high bit-rate data transfer. We use vacuum fluctuations measured by seven homodyne detectors as quantum randomness sources, multiplexed using a single integrated optical device. We obtain a real-time random number generation rate of 3.08 Gbit/s, from only 27.5 MHz of sampled detector bandwidth. Furthermore, we take advantage of the multiplexed nature of our system to demonstrate an unseeded strong extractor with a generation rate of 26 Mbit/s.
The exponential growth of data transmission and processing speeds in modern digital infrastructure requires entropy sources capable of producing large volumes of true randomness for information security. Chaotic emissions from semiconductor lasers are attractive in this context because of their fast dynamics and nonrepetitive behavior. Their spectral bandwidth, however, is typically limited to several tens of gigahertz, which constrains the achievable entropy rate and makes ultrafast random bit generation difficult without substantial post-processing. Here, we demonstrate a chaos-based entropy source that employs optical heterodyning between the chaotic emission from a semiconductor laser and an optical frequency comb, yielding a bandwidth exceeding 100 GHz and an experimentally verified single-channel entropy rate of 1.86 Tb/s. By directly extracting multiple bits from the digitized output of the entropy source, we achieve a single-channel random bit generation rate of 1.536 Tb/s, while four-channel parallelization reaches 6.144 Tb/s with no observable interchannel correlation. This linear scalability suggests that aggregate throughput could reach hundreds of terabits per second with additional parallel channels. The broadband, low-overhead photonic architecture presented here provides a viable route to real-time, ultrafast random bit generation with broad implications for secure communications, high-performance AI computing, and large-scale data analytics.