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arXiv:2509.05573 · Applied Physics Letters

Generation of correlated quantum random number sequences with bright twin beams

Anjanish Shekar, Chirang R. Patel, Jerin A. Thachil, Ashok Kumar

Published Sep 8, 2025• 3 citations
arXivHTMLPDF

Abstract

Quantum random number generators play a vital role in securing communication and encryption. In the present work, we have produced bright twin beams using four-wave mixing in a double-Λ configuration in rubidium-85 vapor and generated two strings of highly correlated random numbers. The randomness originates from the probabilistic nature of the intensity fluctuations of the twin beams and the quantum correlations are certified by measuring the intensity-difference squeezing in the generated twin beams. At an analysis frequency of 2 MHz, we have measured 95% correlation between the random intensity fluctuations of the twin beams. We observe over 5 bits/sample of entropy from the quantum fluctuations of the twin beams. Furthermore, to extract identical strings of random numbers, post-selection of the binned data and hashing algorithms are used, leading to a binary string of random numbers at a rate of 6 Mbps that passes standard statistical tests from NIST and TestU01. Here, the simplicity of generating bright twin beams shows the potential of this method in quantum cryptography and quantum communication.

DOI
10.1063/5.0279909

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•Aug 17, 2016•0 citations
Quantum random number generators play a vital role in securing communication and encryption. In the present work, we have produced bright twin beams using four-wave mixing in a double-Λ configuration in rubidium-85 vapor and generated two strings of highly correlated random numbers. The randomness originates from the probabilistic nature of the intensity fluctuations of the twin beams and the quantum correlations are certified by measuring the intensity-difference squeezing in the generated twin beams. At an analysis frequency of 2 MHz, we have measured 95% correlation between the random intensity fluctuations of the twin beams. We observe over 5 bits/sample of entropy from the quantum fluctuations of the twin beams. Furthermore, to extract identical strings of random numbers, post-selection of the binned data and hashing algorithms are used, leading to a binary string of random numbers at a rate of 6 Mbps that passes standard statistical tests from NIST and TestU01. Here, the simplicity of generating bright twin beams shows the potential of this method in quantum cryptography and quantum communication.
We produce two strings of quantum random numbers simultaneously from the intensity fluctuations of the twin beams generated by a nondegenerate optical parametric oscillator. Two strings of quantum random numbers with bit rates up to 60 Mb/s are extracted simultaneously with a suitable post-processing algorithm. By post-selecting the identical data from two raw sequences and using a suitable hash function, we also extract two strings of identical quantum random numbers. The obtained random numbers pass all NIST randomness tests. The presented scheme shows the feasibility of generating quantum random numbers from the intensity of a macroscopic optical field.
We describe a dual-entropy-source quantum random number generator based on atomic spontaneous emission. Using the intensity fluctuations of a coherent beam to modulate the detuning frequency of the driving field, the atomic ensemble exhibits larger fluctuations of the spontaneous emission noise. The quantum-to-classical-noise ratio of the measured noise is increased to 10.14 dB. After post-processing, a string of random numbers at rates up to 5.12 Mb/s is extracted, which passes all the NIST tests. The presented scheme shows the feasibility to combine multiple independent randomness sources to produce secure quantum random bits.
Generating high-speed, verifiable random numbers is a fundamental requirement for cryptography, large-scale stochastic simulations, and secure quantum communication. Here, we present a robust quantum random number generator that utilizes the spatial distribution of quantum fluctuations captured by an electron-multiplying charge-coupled device operated in high-speed kinetic mode. Through rigorous detector calibration and shot-noise analysis, we characterize the spatial quantum noise obtained from the spatial intensity fluctuations of the coherent states of light. Such quantum noise serves as a high-entropy source, enabling an instantaneous random bit generation rate of 5.92 Gbps without algorithmic randomness extraction in the present configuration. The sustained output rate is, however, limited to 7.5 Mbps by the bandwidth of the serial electronic readout. The generated sequences successfully pass the NIST SP 800-22 and Marsaglia Diehard statistical test suites, confirming the high quality and unpredictability of the entropy source.
Using a nondegenerate four-wave mixing process based on a double-$\mathrm{\ensuremath{\Lambda}}$ scheme in hot cesium vapor, we generate quantum correlated twin beams with a maximum intensity-difference squeezing of 6.5 dB. The substantially improved squeezing can be mainly attributed to very good frequency and phase-difference stability between the pump and probe beams in our experiment. Intensity-difference squeezing can be observed within a wide experimental parameter range, which guarantees its robust generation. Since this scheme produces multi-spatial-mode twin beams at the Cs D1{D}_{1}D1​ line, it is of interest for experiments involving quantum imaging and coherent interfaces between atomic and solid-state systems.
We have built a compact light source for bright squeezed twin-beams at 795nm based on four-wave-mixing in atomic 85Rb vapor. With a total optical power of 400mW derived from a free running diode laser and a tapered amplifier to pump the four-wave-mixing process, we achieve 2.1 dB intensity difference squeezing of the twin beams below the standard quantum limit, without accounting for losses. Squeezed twin beams generated by the type of source presented here could be used as reference for the precise calibration of photodetectors. Transferring the quantum correlations from the light to atoms in order to generate correlated atom beams is another interesting prospect. In this work we investigate the dispersion that is generated by the employed fourwave- mixing process with respect to bandwidth and dependence on probe detuning. We are currently using this squeezed light source to test the transfer of spatial information and quantum correlations through media of anomalous dispersion.
We have built a compact light source for bright squeezed twin-beams at 795\,nm based on four-wave-mixing in atomic 85^{85}85Rb vapor. With a total optical power of 400\,mW derived from a free running diode laser and a tapered amplifier to pump the four-wave-mixing process, we achieve 2.1\,dB intensity difference squeezing of the twin beams below the standard quantum limit, without accounting for losses. Squeezed twin beams generated by the type of source presented here could be used as reference for the precise calibration of photodetectors. Transferring the quantum correlations from the light to atoms in order to generate correlated atom beams is another interesting prospect. In this work we investigate the dispersion that is generated by the employed four-wave-mixing process with respect to bandwidth and dependence on probe detuning. We are currently using this squeezed light source to test the transfer of spatial information and quantum correlations through media of anomalous dispersion.