Our work aims to introduce an FPGA-based electronics architecture designed to enhance the security of quantum key distribution (QKD) networks. The core focus is on integrating a true random number generator (TRNG) IP in an FPGA-based QKD control electronics implemented on Xilinx’s ZYNQ UltraScale+ based FPGA boards. The work presents the challenges in integrating an existing TRNG IP with QKD FPGA design, different bit and timing requirements, the subsequent speed mismatch issues, support for multiple QKD protocols (Coherent One-Way (CoW) and Differential Phase Shift (DPS)) and user-defined QKD implementations. The integrated design also supports external QRNG/TRNG over USB/Ethernet.
Our work aims to introduce an FPGA-based electronics architecture designed to enhance the security of quantum key distribution (QKD) networks. The core focus is on integrating a true random number generator (TRNG) IP in an FPGA-based QKD control electronics implemented on Xilinx’s ZYNQ UltraScale+ based FPGA boards. The work presents the challenges in integrating an existing TRNG IP with QKD FPGA design, different bit and timing requirements, the subsequent speed mismatch issues, support for multiple QKD protocols (Coherent One-Way (CoW) and Differential Phase Shift (DPS)) and user-defined QKD implementations. The integrated design also supports external QRNG/TRNG over USB/Ethernet.
Quantum Key Distribution (QKD) is an emerging field in private key cryptography. Recent advancements in quantum cryptography are focused on developing more secure protocols, particularly in response to the real time implementations of quantum hacking. Our research article focuses on Measurement-Device-Independent (MDI) and Twin-Field (TF) Quantum Key Distribution protocols, addressing the challenges associated with their implementation. We have discussed the implementation of a discrete phase randomization technique and phase slicing for Twin-Field (TF) Quantum Key Distribution, along with the integration of a random number generator (RNG). In our work, we designed and implemented initial quantum state preparation and the control electronics for an advanced Quantum Key Distribution system using an FPGA board.
Most hardware "true" random number generators (TRNGs) take advantage of the thermal agitation around a flip-flop metastable state. In field programmable gate arrays (FPGAs), the classical TRNG structure uses two clocks, either from a PLL or from ring oscillators, in order to sample one by the other. This creates good TRNGs albeit limited in frequency by the interference rate which cannot exceed a few Mbit/s. This article presents an architecture allowing higher bit rates while maintaining provable unconditional security. This requirement becomes stringent for secure communication applications such as the cryptographic quantum key distribution (QKD) protocols. The proposed architecture is very simple as it is based on an open loop structure without any specific component such as PLLs.
Quantum technologies are rapidly transforming the landscape of secure communication and computation by exploiting the fundamental principles of quantum mechanics. Among these, Quantum Key Distribution (QKD) offers an unprecedented level of security in communications, provided by physical principles rather than computational assumptions. However, the realization of scalable and practical quantum networks remains challenging. Key technological hurdles include the need for high-sensitivity and high-speed single-photon detectors, stable and integrated optical platforms, and robust and fast true random number generators. Overcoming these challenges is essential to bridge the gap between laboratory demonstrations and the real-world deployment of quantum networks. This thesis addresses some of these critical issues through work in single-photon detection technologies, integrated QKD system implementation, and high-speed Quantum Random Number Generators (QRNGs). Single-Photon Avalanche Diodes are fundamental detectors for quantum technologies, enabling high-sensitivity measurements at the single-photon level. This thesis investigates the operating principles, limitations, and advancements of Single-Photon Avalanche Diodes, with a focus on high-speed dual-anode designs. Their photon detection efficiency, dark count rate, afterpulsing probability, and timing jitter are analyzed, while optimized control electronics and capacitance management strategies are developed. The characterization of Single-Photon Avalanche Diodes demonstrates their suitability for quantum communication, particularly in quantum key distribution and asynchronous heralded photon sources, with pathways for further improvements in speed and integration. Building on these detector technologies, a proof-of-principle integrated quantum key distribution system based on the BB84 protocol is presented. The system incorporates time-bin encoding, decoy-state methods, and photonic integrated circuits for both transmitter and receiver. Key challenges, such as chromatic dispersion and interferometer stability, are addressed through novel circuit and system-level designs. System-level testing and field deployment validate the feasibility of compact, high-performance integrated quantum key distribution implementations. Finally, the thesis explores quantum random number generation through semi-device-independent protocols. An experimental homodyne-based SDI-QRNG is realized, supported by custom transimpedance amplifier design and photonic integrated circuit integration. The setup achieves high bandwidth, strong quantum-to-classical noise separation, and stable operation, enabling practical random number generation rooted in fundamental quantum processes. Overall, this work advances the development of integrated quantum technologies by improving room-temperature single-photon detection, demonstrating scalable QKD prototypes, and implementing a high-speed QRNG. Together, these contributions pave the way toward secure, integrated quantum communication systems and practical quantum information applications ready to deploy in real world networks.
Cryptography is evolving to meet the demands of future cyber technologies, but classical cryptographic methods remain vulnerable to interception. Cryptographic techniques struggle to address the evolving landscape of cybersecurity threats, Quantum Key Distribution (QKD) emerges as a superior alternative, leveraging quantum mechanics principles such as superposition and entanglement for secure key exchanges. This chapter details the implementation of a Quantum True Random Number Generator (QTRNG) using fundamental single-qubit operation including Hadamard (H), Rotation (RZ) and square-root NOT (SX) gates using IBM Quantum Platform. We evaluate the integration of this QTRNG across several discrete variable QKD protocols: BB84, B92, E91, T22, Differential Phase Shift, and SARG04. The study focuses on how the QTRNG contributes to the randomness and security of these protocols, demonstrating its effectiveness in producing high-quality quantum keys that meet rigorous cryptographic standards.
This thesis work is about the realization of hardware and software systems for Quantum Random Number Generation (QRNG) and Quantum Key Distribution (QKD). Such systems were developed to guarantee a full functionality for a broader investigation of these two cutting edge applications of Quantum Information field. The thesis describes in details both the hardware and the software that were developed for FPGA-CPU board, Time-to-Digital converter (TDC) devices and computers, along with QRNG and QKD specific applications and their results. Randy was the first FPGA-based QRNG device to be developed; it uses a light source attenuated to single-photon level and one single-photon avalanche diode (SPAD). From the sampling of the SPAD electrical signal, the device produces random numbers through dedicated generation protocols and through the Peres unbiasing algorithm in order to maximize the output generation bit rate. Furthermore, the device allows to generate real time random numbers. This feature is used for the time setting of electro-optical components for extending Wheeler’s delayed-choice experiment to space. The same techniques were applied to a second device, LinoSPAD; it combines an FPGA-chip and a CMOS-SPADs array. Moreover, in this device, a TDC improves the photon detection time accuracy. Along with a dedicated post-processing based on Zhou-Bruk algorithm, the TDC allowed to reach a final bit rate equivalent to 300 Mbit/s. As far as QKD systems are concerned, within the collaboration among the University of Padova, the Italian Space Agency (ASI) with the Matera Laser Ranging Observatory (MLRO) and the Chinese Academy of Sciences (CAS) a TDC device management software was developed. The project aim is to realize a quantum cryptographic key exchange between the Chinese satellite Micius and MLRO. The software was designed to manage the entire data acquisition synchronized with UTC time. Furthermore, another software was designed to deal with electro-optomechanical and electro-optical components. The software is aim at the time-variant compensation of the beam angular changes through the optical path. Once again, within a collaboration between ASI and University of Padova, a full free space QKD system over tenths of kilometers was developed. It required the design of various components. This work describes the QKD source along with the dedicated FPGA board design. Such board generates the electrical impulses to control the qubit laser along with the electro-optic phase and intensity modulators.