Tommaso Bertapelle

Continuous‑Variable Quantum Key Distribution (CV‑QKD) and Quantum Random Number Generation (CV‑QRNG) are crucial technologies relying on shot‑noise‑limited coherent detection to enable secure communication and high‑speed randomness generation. Integrated photonics plays a central role in advancing these technologies, offering compact, scalable, and efficient implementations. In this work, we introduce Femtosecond Laser Micromachining (FLM) on borosilicate glass as a novel platform for Photonic Integrated Circuits (PICs) tailored to coherent detection in quantum information processing. Using off‑chip detectors, we exploit the versatility of FLM to realize a PIC designed for CV‑QKD and CV‑QRNG. The device features fully tunable optical components, low insertion loss ($\leq$ 1.28 dB), polarization‑insensitive operation, and a Common‑Mode Rejection Ratio (CMRR) exceeding 73 dB. These capabilities enable the experimental demonstration of a Source‑device‑Independent CV‑QRNG with a secure rate of 42.74 Gbps and a QPSK‑based CV‑QKD system achieving a 3.2 Mbit/s secret key rate. Our results establish FLM as a promising integrated‑photonics platform for scalable, high‑performance quantum communication systems.

A wide range of applications require, by hypothesis, to have access to a private and genuine random source. Quantum Random Number Generators (QRNGs) are currently the sole technology capable of producing true randomness. Nevertheless, other factors must be considered when addressing real-world use cases, and the bulkiness of current implementations significantly limits their adoption. In this work, we present a high-performance source-device independent QRNG leveraging a custom-made integrated silicon photonic chip. The proposed scheme exploits the properties of a heterodyne receiver to enhance security and integration to promote spatial footprint reduction while simplifying its implementation. Such characteristics could represent a significant advancement toward the development of generators better suited to meet the demands of portable and space applications. Indeed, the system can deliver secure random numbers at a rate greater than 20 Gbps with a reduced encumbrance.

Key exchange over an untrusted communication channel is a crucial step in modern cryptographic protocols, yet current approaches rely on computational assumptions to ensure their security. However, these assumptions may be undermined by an adversary possessing quantum computational capabilities. Quantum Key Distribution (QKD), both in its Discrete Variable (DV) and Continuous Variable (CV) format, is a way to counter this threat. By exploiting the principles of quantum mechanics, QKD enables the development of unconditionally secure protocols, providing a lasting solution that can withstand adversaries regardless of their computational resources. Between DV and CV, the latter is particularly appealing if speed and compatibility with the current fiber telecom infrastructure are considered. In fact, CV-QKD systems can benefit from coherent receivers and widely accessible fiber-based commercial telecom components. Despite this, several practical tasks must be addressed to enable such systems targeting field-deployed real-world scenarios. Among these are the integration of a Quantum Random Number Generator, real-time estimation of key system parameters necessary to compute the Secret Key Rate and network reconfigurability. This study presents a CV-QKD architecture integrating a coherent receiver at the transmitter, enabling secure quantum randomness generation and in-line estimation of key parameters for secret-key-rate computation, advancing the deployment over existing telecom networks.

Quantum Random Number Generators (QRNGs) are essential components for modern cryptography, as they are a practical source of true randomness, without which the security of such protocols cannot be guaranteed. Among the proposed schemes, Semi-Device-Independent QRNGs (SDI-QRNGs) based on photon-number constraints offer an appealing balance of security, speed, and experimental simplicity, but demonstrations have so far focused mainly on binary encoding and conditional min‑entropy certification. In this work, we report the first experimental implementation of a Continuous‑Variable SDI‑QRNG in a prepare‑and‑measure configuration building on the SDP‑based (Semi-Definite Programming) framework of Ref.~\cite{carceller2025}. This approach allows us to directly lower‑bound the conditional Shannon entropy, employ more complex modulation formats, and apply entropy‑accumulation techniques beyond the i.i.d. assumption. The experiment combines a low-loss integrated photonic heterodyne receiver with a simple transmitter built from commercial components, generating coherent‑state Quadrature-Phase-Shift-Keying (QPSK) modulation, to preserve experimental practicality while enabling high‑speed operation.

We present a versatile hybrid encoder for quantum key distribution that supports both discrete variable (DV) and continuous variable (CV) protocols. The encoder, based on an iPOGNAC modulator, utilizes commercial off-the-shelf components and can be reconfigured for efficient polarization modulation in DV protocols or polarization-independent phase modulation in CV protocols. This innovative design enhances flexibility, enabling the selection of the most efficient protocol based on link parameters. We experimentally realized the proposed device and tested it with both DV and CV receivers to demonstrate its performance.