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Optics Letters

Dual-entropy-source quantum random number generation based on spontaneous emission

Qiang Zhang, Dehuan Kong, Yebing Wang, Hongxin Zou, Hong Chang

Published Dec 5, 2019• 4 citations
Publisher

Abstract

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.

DOI
10.1364/ol.382067

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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.
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.
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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.
Quantum random number generators (QRNGs) harness the intrinsic randomness in measurement processes: the measurement outputs are truly random, given the input state is a superposition of the eigenstates of the measurement operators. In the case of trusted devices, true randomness could be generated from a mixed state ρ so long as the system entangled with ρ is well protected. We propose a random number generation scheme based on measuring the quadrature fluctuations of a single mode thermal state using an optical homodyne detector. By mixing the output of a broadband amplified spontaneous emission (ASE) source with a single mode local oscillator (LO) at a beam splitter and performing differential photo-detection, we can selectively detect the quadrature fluctuation of a single mode output of the ASE source, thanks to the filtering function of the LO. Experimentally, a quadrature variance about three orders of magnitude larger than the vacuum noise has been observed, suggesting this scheme can tolerate much higher detector noise in comparison with QRNGs based on measuring the vacuum noise. The high quality of this entropy source is evidenced by the small correlation coefficients of the acquired data. A Toeplitz-hashing extractor is applied to generate unbiased random bits from the Gaussian distributed raw data, achieving an efficiency of 5.12 bits per sample. The output of the Toeplitz extractor successfully passes all the NIST statistical tests for random numbers.
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.
Quantum coherence serves as a fundamental resource for generating intrinsic randomness, yet the quantification of randomness in quantum random number generators (QRNGs) based on spontaneous emission has remained largely phenomenological. Existing randomness analysis lacks rigorous adversarial models and a clear characterization of the role of quantum coherence in these systems. In this work, we develop a comprehensive quantum information-theoretic framework for randomness generation in spontaneous emission processes. We characterize two distinct eavesdropping strategies: one where the adversary directly accesses the atom ensemble, and the other where the adversary accesses only its purification. Our analysis reveals that when randomness is generated through single-photon detection and temporal mode measurements, the QRNG is vulnerable to the first adversary scenario, though it still guarantees a lower bound on intrinsic randomness against the second adversary scenario even under maximal information leakage from the atoms. In contrast, QRNGs based on spatial mode detection and phase fluctuations demonstrate security against both types of adversaries, providing robust randomness generation. Furthermore, we provide a quantitative calculation of intrinsic randomness for these spontaneous-emission-based QRNG schemes.