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arXiv:2004.08344 · Physical Review Applied

Semi-Device-Independent Heterodyne-Based Quantum Random-Number Generator

Marco Avesani, Hamid Tebyanian, Paolo Villoresi, Giuseppe Vallone

Published Mar 11, 2021• 48 citations
arXivHTMLPDF

Abstract

Randomness is a fundamental feature of quantum mechanics, which is an invaluable resource for both classical and quantum technologies. Practical quantum random-number generators (QRNGs) usually need to trust their devices, but their security can be jeopardized in the case of imperfections or malicious external actions. In this work, we present a robust implementation of a semi-device-independent QRNG that guarantees both security and fast generation rates. The system works in a prepare-and-measure scenario, where measurement and source are uncharacterized, but a bound on the energy of the prepared states is assumed. Our implementation exploits heterodyne detection, which offers increased generation rate and improved long-term stability compared to alternative measurement strategies. In particular, due to the tomographic properties of heterodyne measurement, we can compensate for fast phase fluctuations via postprocessing, avoiding complex active phase-stabilization systems. As a result, our scheme combines high security and speed with a simple setup featuring only commercial-off-the-shelf components, making it an attractive solution in many practical scenarios.

DOI
10.1103/physrevapplied.15.034034

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Randomness is a fundamental feature of quantum mechanics, which is an invaluable resource for both classical and quantum technologies. Practical quantum random-number generators (QRNGs) usually need to trust their devices, but their security can be jeopardized in the case of imperfections or malicious external actions. In this work, we present a robust implementation of a semi-device-independent QRNG that guarantees both security and fast generation rates. The system works in a prepare-and-measure scenario, where measurement and source are uncharacterized, but a bound on the energy of the prepared states is assumed. Our implementation exploits heterodyne detection, which offers increased generation rate and improved long-term stability compared to alternative measurement strategies. In particular, due to the tomographic properties of heterodyne measurement, we can compensate for fast phase fluctuations via postprocessing, avoiding complex active phase-stabilization systems. As a result, our scheme combines high security and speed with a simple setup featuring only commercial-off-the-shelf components, making it an attractive solution in many practical scenarios.
Quantum random number generators (QRNGs) produce true random numbers based on the inherent randomness of quantum theory, rendering them a foundational segment of quantum cryptography. Distinguished from trusted-device QRNGs whose security depends on characterized devices, semi-device-independent (semi-DI) QRNGs permit partial devices to be defective or even maliciously manipulated, which achieves a good trade-off between generation rate and security. In this paper, we propose a semi-DI QRNG that resists general attacks while accounting for finite-size effects. The protocol requires no rigorous characterization of the source and measurement devices other than limiting the energy of the emitted states, significantly reducing the demands on practical QRNG systems. Leveraging the tight Kato inequality for correlated variables, we show that our protocol generates more randomness than it consumes. Furthermore, we demonstrate the scheme on a continuous-variable system with ternary inputs of states. Heterodyne detection is employed to enable phase compensation through data postprocessing, alleviating the stringent requirement on system stability. The system operates at 100 MHz, achieving a net random number generation rate of 1.165 Mbps at 5.3x10^9 rounds. Our work offers a promising approach to achieve both the robust security and high generation rate with a simple experimental setup.
Semi-device-independent QRNG frameworks represent a particularly attractive approach, combining strong security guarantees with high randomness generation rates while relying only on reduced and practical physical assumptions. A recently proposed approach based on photon-number constraints is particularly suited to photonic implementations, where these assumptions can be easily assessed experimentally. Here, we experimentally demonstrate a quantum random number generator within this framework, enabling the direct computation of lower bounds on the certifiable Shannon entropy via semidefinite relaxation techniques. When combined with entropy accumulation methods, this approach enables finite-size randomness certification without assuming independent and identically distributed rounds. We realize the protocol using a four-state coherent-state constellation symmetrically distributed in phase space and measured by heterodyne detection, certifying 0.223 bit per measurement, which is the highest value reported to date for a continuous-variable semi-device-independent QRNG. The implementation combines a low-loss integrated photonic heterodyne receiver with a simple transmitter assembled from commercial components, providing a practical and high-speed architecture for semi-device-independent randomness generation.
Random numbers are commonly used in many different fields, ranging from simulations in fundamental science to security applications. In some critical cases, as Bell's tests and cryptography, the random numbers are required to be both private and to be provided at an ultra-fast rate. However, practical generators are usually considered trusted, but their security can be compromised in case of imperfections or malicious external actions. In this work we introduce an efficient protocol which guarantees security and speed in the generation. We propose a source-device-independent protocol based on generic Positive Operator Valued Measurements and then we specialize the result to heterodyne measurements. Furthermore, we experimentally implemented the protocol, reaching a secure generation rate of 17.42 Gbit/s, without the need of an initial source of randomness. The security of the protocol has been proven for general attacks in the finite key scenario.
Abstract Semi-device independent (Semi-DI) quantum random number generators (QRNGs) gained attention for security applications, offering an excellent trade-off between security and generation rate. This paper presents a proof-of-principle time-bin encoding semi-DI QRNG experiments based on a prepare-and-measure scheme. The protocol requires two simple assumptions and a measurable condition: an upper-bound on the prepared pulses’ energy. We lower-bound the conditional min-entropy from the energy-bound and the input–output correlation, determining the amount of genuine randomness that can be certified. Moreover, we present a generalized optimization problem for bounding the min-entropy in the case of multiple input and outcomes, in the form of a semidefinite program. The protocol is tested with a simple experimental setup, capable of realizing two configurations for the ternary time-bin encoding scheme. The experimental setup is easy-to-implement and comprises commercially available off-the-shelf components at the telecom wavelength, granting a secure and certifiable entropy source. The combination of ease-of-implementation, scalability, high security level and output-entropy, make our system a promising candidate for commercial QRNGs.
Generating certifiably random bit sequences using quantum devices is a fundamental challenge for cryptography, particularly as applied to secure communication. The device-independent approach offers the best security, but is impractical. This study presents a quantum random-number generator (QRNG) that is simple and achieves high bit rates, yet requires only mild assumptions (almost no trust) regarding the setup. This protocol offers a promising solution for the next generation of QRNGs, combining ease of implementation, commercially viable rates, and strong security.