Quantum random number generators (QRNGs) play an increasingly important role in cryptography systems. Specifically, QRNG performed in prepare-and-measure scenarios with independent devices has attracted intensive study, since it can be intrinsically loss tolerant and its assumptions on devices seem to be quite natural. However, the estimations of min-entropy given in previous works are not optimal. As a result, the performance of quantum randomness certification in practice is still severely depressed. Here, we present a novel method to estimate the min-entropy through developing a reduced device model and proving its equivalence to the original one. Benefitting from this reduction, we can solve the min-entropy estimation problem using mixed integer programming effectively. Furthermore, we derive an optimal bound of analytic form in the case that constraints are made up of symmetric observed probabilities. Simulation results show that our work gives an optimal solution in this case and brings a significant performance improvement compared to previous works.
Quantum random number generators (QRNGs) play an increasingly important role in cryptography systems. Specifically, QRNG performed in prepare-and-measure scenarios with independent devices has attracted intensive study, since it can be intrinsically loss tolerant and its assumptions on devices seem to be quite natural. However, the estimations of min-entropy given in previous works are not optimal. As a result, the performance of quantum randomness certification in practice is still severely depressed. Here, we present a novel method to estimate the min-entropy through developing a reduced device model and proving its equivalence to the original one. Benefitting from this reduction, we can solve the min-entropy estimation problem using mixed integer programming effectively. Furthermore, we derive an optimal bound of analytic form in the case that constraints are made up of symmetric observed probabilities. Simulation results show that our work gives an optimal solution in this case and brings a significant performance improvement compared to previous works.
Quantum random number generation attracts considerable attention, since its randomness inherently originates in quantum mechanics, but not mathematical assumptions. Randomness certification, e.g. entropy estimation, becomes a key issue in the context of quantum random number generation protocol. We study a self-testing protocol based on dimension witness, with the assumption of independent devices. It addresses the random number extraction problem in a practical prepare-and-measure scenario with uncharacterized devices. However, the lower bound of min-entropy as a function of dimension witness is not tight in existing works. We present a tighter bound of analytic form, by introducing the Lagrangian multiplier method to closely analyze the optimization problem on average guessing probability. Through simulation, it turns out that a significantly higher random number generation rate can be achieved in practice.
For quantum random number generators (QRNGs), strong security guarantees can be obtained under various assumptions. The most well-known assumptions are the non-signalling assumption (needed for device-independent (DI) QRNG) and post-quantum computational assumptions (needed for computationally bounded single-prover QRNG protocols). In this work, we study a third model: a simple prepare-and-measure QRNG whose security relies on physically motivated energy constraints. This physically motivated set-up allows for easier implementations of QRNGs and can supply better rates.
So far, previous works that studied the energy-constrained model either assumed that the adversary is classical in their security proof or supplied relatively weak bounds on the certified randomness, by bounding the conditional min-entropy. In this work, we prove a new, essentially tight, lower bound on the single-round von Neumann entropy against adversaries holding both classical and quantum side-information. Our work reveals that working with the von Neumann entropy, rather than the min-entropy, in the quantum case can lead to a major improvement, nearly matching the classical bound in many cases. We further study the robustness of our entropy bound. Since the single-round von Neumann entropy is the main quantity of interest when characterizing the key rate of QRNGs, our bound establishes the main ingredient for rigorous security proofs against general quantum attacks in this framework.
How to generate genuine quantum randomness from untrusted devices is an important problem in quantum information processing. Inspired by previous work on a self-testing quantum random number generator [T. Lunghi et al., Phys. Rev. Lett. 114, 150501 (2015)], we present a method to generate quantum randomness from a prepare-and-measure scenario with independent devices. In existing protocols, the quantum randomness depends only on a witness value (e.g., Clauser-Horne-Shimony-Holt value), which is calculated with the observed probabilities. Differently, here all the observed probabilities are directly used to calculate the min-entropy in our method. Through numerical simulation, we find that the min-entropy of our proposed scheme is higher than that in the previous work when a typical untrusted Bennett-Brassard 1984 (BB84) setup is used. Consequently, thanks to the proposed method, more genuine quantum random numbers may be obtained than before.
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.
Abstract Quantum technologies promise information processing and communication technology advancements, including random number generation (RNG). Using Bell inequalities, a user of a quantum RNG hardware can certify that the values provided by an untrusted device are truly random. This problem has been extensively studied for von Neumann and min-entropy as a measure of randomness. However, in this paper, we analyze the feasibility of such verification for Shannon entropy. We investigate how the usability of various Bell inequalities differs depending on the presence of noise. Moreover, we present the benefit of certification for Shannon compared to min-entropy, as well as the tight analytical lower bound for Shannon entropy in randomness certification.
For practical applications of quantum randomness generation, it is important to certify and further produce a fixed block of fresh random bits with as few trials as possible.Consequently, protocols with high finite-data efficiency are preferred.To yield such protocols with respect to quantum side information, we develop quantum probability estimation.Our approach is applicable to device-independent as well as device-dependent scenarios, and it generalizes techniques from previous works [Miller and Shi, SIAM J. Comput. 46, 1304 (2017); Arnon-Friedman et al., Nat. Commun. 9, 459 (2018)].Quantum probability estimation can adapt to changing experimental conditions, allows stopping the experiment as soon as the prespecified randomness goal is achieved, and can tolerate imperfect knowledge of the input distribution.Moreover, the randomness rate achieved at constant error is asymptotically optimal.For the device-independent scenario, our approach certifies the amount of randomness available in experimental results without first searching for relations between randomness and violations of fixed Bell inequalities.We implement quantum probability estimation for device-independent randomness generation in the CHSH Bell-test configuration, and we show significant improvements in finite-data efficiency, particularly at small Bell violations which are typical in current photonic loophole-free Bell tests.