Metrological Analysis of a QRNG Based on the Quandela Photonic Quantum Computer
Muriel A. de Souza, F. P. Agostini, Luiz Vicente Gomes Tarelho
Abstract
Quantum random number generators (QRNGs) play a crucial role in cryptography, secure communications, and stochastic simulations. This study presents the metrological characterization of a QRNG implemented on the Quandela photonic quantum computer, available via the cloud. The system generates random sequences using single photons and beam splitters, where quantum superposition ensures a fundamentally probabilistic outcome. A key aspect of this characterization involves defining the sample size and the number of qubits used. The Quandela quantum processor operates with up to six qubits, corresponding to six photons in twelve optical modes. However, the simultaneous use of multiple photons can introduce unintended correlations due to quantum interference, affecting the quality of randomness. To ensure independent bit generation, experiments were conducted with a single photon per measurement, producing one-bit outcomes per detection event. The analysis focuses on repeatability and reproducibility, examining the statistical properties of the generated sequences. Raw sequences underwent randomness testing using NIST SP800-22 and entropy assessment with NIST SP800-90B. Initial results indicate that raw sequences exhibit biases due to imperfections in single-photon sources and optical elements. The sequences generated by the Quandela photonic quantum processor failed most NIST SP800-22 tests, including Frequency (Global and Block), Runs, and Approximate Entropy, with six tests showing a 100% failure rate. Additionally, under the NIST SP800-90B evaluation, 100% of the raw sequences failed the independence and identically distributed (IID) test, highlighting strong correlations and statistical dependencies. To enhance randomness quality, post-processing techniques were applied, including Von Neumann and the combination Samuelson + Von Neumann extractors. These methods significantly improved bit balance and reduced statistical dependencies. After post-processing, all sequences passed the NIST SP800-90B IID test, and the entropy per bit increased to 0.771 ± 0.005 for the Ascella processor, ensuring improved randomness quality. The findings highlight the metrological challenges in QRNGs based on photonic quantum processors, emphasizing the need for rigorous statistical validation. Despite system-specific noise, the quantum origin of randomness remains preserved, ensuring that the extracted sequences retain their fundamental unpredictability. Additionally, limitations associated with photonic quantum systems, such as hardware imperfections, photon losses, and optical misalignment, are discussed in the context of their impact on randomness quality. Despite these limitations, rigorous statistical validation and post-processing enable the generation of high-quality random sequences suitable for cryptographic protocols, secure key distribution, and high-performance computing This study reinforces the importance of metrology in quantum technologies, providing a structured methodology for optimizing QRNG reliability and performance.