Davide G. Marangon

Random numbers play a crucial role in information technology, particularly as digital communication capacity continues to expand. Consequently, the need for secure and high-rate random number generation has become increasingly urgent. While integrated photonics technology holds promise for mass-producing optoelectronic quantum random number generators (QRNGs), there remains a challenge in developing fast, robust, and scalable solutions suitable for industrial deployment. Addressing this challenge, we present a fast QRNG solution in this study, leveraging a photonic integrated circuit (PIC) directly embedded onto a versatile electronic platform. Designed to withstand real-world applications, our PIC is packaged to align with industrial electronic assembly lines. To rigorously assess scalability and stability, these generators underwent week-long periods of continuous GHz operation. Furthermore, a QRNG was integrated into a quantum key distribution system, where despite operating in an uncontrolled environment, minimal variations in physical randomness were observed over 38 days, as measured from 2.9 million histograms. Finally, we implemented a security model for the QRNGs, enabling rate adjustment to match the actual randomness content and demonstrating secure generation at 2 Gbit/s.

Integrated photonics presents an opportunity for low-cost and highly-reproducible quantum cryptographic systems. However, due to numerous challenges such as packaging, power consumption and interfacing multiple chips in real, a standalone deployable photonic integrated system is still missing. Here we address all these challenges to present a real-time quantum communication system using integrated photonics. The system operated without intervention over multiple days and is capable of secure key rates of > 470 kbps over 10 km of fiber

Random numbers are a fundamental ingredient in fields such as simulation, modeling, and cryptography. Good random numbers should be independent and uniformly distributed. Moreover, for cryptographic applications, they should also be unpredictable. A fundamental feature of quantum theory is that certain measurement outcomes are intrinsically random and unpredictable. These can be harnessed to provide unconditionally secure random numbers. We demonstrate a real-time self-testing source-independent quantum random-number generator (SI QRNG) that uses squeezed light as a source. We generate secure random numbers by measuring the quadratures of the electromagnetic field without making any assumptions about the source other than an energy bound; only the detection device is trusted. We use homodyne detection to measure alternately the Q and P conjugate quadratures of our source. P measurements allow us to estimate a bound on any classical or quantum side information that a malicious eavesdropper may obtain. This bound gives the minimum number of secure bits we can extract from the Q measurement. We discuss the performance of different estimators for this bound. We operate this QRNG with a squeezed-state source and compare its performance with a thermal-state source. This is a demonstration of a QRNG using a squeezed state, as well as an implementation of real-time quadrature switching for a SI QRNG.

We investigate the feasibility of satellite-to-ground quantum key distribution (QKD) at multi-GHz clock rates, where secure key generation time is constrained, due to LEO satellite overpasses (≈ 300 s). Higher repetition rates present an immediate route to increased secure key rate (SKR), though performance is limited by detector jitter, coupling losses, and atmospheric turbulence, depending on the receiver architecture. We combine finite-key modelling, detailed detector timing characterization, adaptive optics (AO) modelling, and real-time free-space QKD experiments at 1 GHz to evaluate practical receiver configurations based on multi-mode fiber-coupled avalanche photodiodes (MMF-APDs) and single-mode fiber-coupled superconducting nano-wire single-photon detectors (SMF-SNSPDs), at projected rates > 1 GHz. The results indicate clear operating regimes: MMF-APDs maximize secure key rates below ∼ 1 GHz, predominantly due to their low coupling loss. However, low-jitter SMF-SNSPDs are required to obtain positive key rates at > 1GHz clock rates (estimated optimal operating point near ∼ 7.55 GHz), though AO correction is required for effective single-mode coupling under turbulence. The experimental and projected results provide realistic design targets for future high-rate satellite QKD systems, while highlighting the technological requirements needed to achieve end-to-end operation beyond the GHz regime.