Entanglement-based quantum key distribution (QKD) offers robust key distribution through intrinsically correlated measurements, ensuring any eavesdropping attempt introduces detectable disturbances. Although practical implementations are primarily limited to fixed fiber networks, extending QKD to mobile platforms like drones or small satellites introduces challenges in optical alignment, weight, and power consumption. This work outlines the core components and architecture for implementing BBM92-based QKD in mobile settings. A compact polarization Sagnac interferometer utilizing a PPKTP crystal provides a stable and efficient method for generating entangled photon pairs. Supporting subsystems include a polarization compensation system, a detector module, and an acquisition, pointing, and tracking (APT) system. To assess performance under realistic conditions, we simulate photon loss, detector efficiency, and quantum bit error rates using the SQUANCH framework. Results show an average key generation rate of 5.43 bits/s, a final secure key length of 45.27 bits per block, and a QBER of 4.5%.
Entanglement-based quantum key distribution (QKD) offers robust key distribution through intrinsically correlated measurements, ensuring any eavesdropping attempt introduces detectable disturbances. Although practical implementations are primarily limited to fixed fiber networks, extending QKD to mobile platforms like drones or small satellites introduces challenges in optical alignment, weight, and power consumption. This work outlines the core components and architecture for implementing BBM92-based QKD in mobile settings. A compact polarization Sagnac interferometer utilizing a PPKTP crystal provides a stable and efficient method for generating entangled photon pairs. Supporting subsystems include a polarization compensation system, a detector module, and an acquisition, pointing, and tracking (APT) system. To assess performance under realistic conditions, we simulate photon loss, detector efficiency, and quantum bit error rates using the SQUANCH framework. Results show an average key generation rate of 5.43 bits/s, a final secure key length of 45.27 bits per block, and a QBER of 4.5%.
Entanglement-based quantum key distribution (QKD) protocols, such as E91 and BBM92, offer strong information-theoretic security and are naturally suited for satellite-to-satellite QKD (SatQKD) links. However, implementing these protocols over long-distance inter-satellite free-space optical (FSO) channels poses critical physical-layer challenges that are not addressed in the existing literature. In particular, photon losses due to beam divergence, pointing errors, and background noise can severely degrade the key generation rate and quantum bit error rate (QBER), especially under narrow receiver field-of-view (FoV) constraints. This paper presents a comprehensive performance analysis of entanglement-based inter-satellite QKD, focusing on photon-level modeling and the impact of practical impairments. We develop analytical expressions for signal detection probabilities, background photon influence, multi-pair emissions, and QBER, incorporating key parameters such as link distance, transmitter tracking jitter, receiver misalignment, and photon pair generation rate. Simulation results reveal the nonlinear sensitivity of system performance to tracking error and FoV limitations, and highlight optimal parameter regimes that jointly maximize secret key rate while maintaining QBER below acceptable thresholds. The proposed model provides actionable design insights for reliable and efficient deployment of entanglement-based SatQKD systems.
Abstract The integration of quantum key distribution (QKD) into data centers represents a promising advance in secure communications. As cyber threats evolve and the volume of sensitive information grows, strengthening intra-data center security has become a strategic necessity for ensuring confidentiality and operational resilience. This paper explores the application of an entanglement-based QKD method for securing intra-connectivity within data centers, focusing on deploying the BBM92 protocol in a controlled environment. We detail the system architecture, technical requirements, and operational considerations, and we report simulation results from a 100-block BBM92 run: an average sifted key of 1224 bits per block, with 25% used for QBER estimation, reconciliation disclosures of 352 bits, and privacy amplification removing an additional 13 bits, yielding a final secure key of 554 bits per block at an average rate of 52 bps. Across the run, 86 keys were delivered to applications, enabling 43 IKEv2/IPsec sessions, with an initial ramp-up before reaching steady, near-linear key service. These findings indicate that entanglement-based QKD can provide robust, quantum-safe key distribution for data center environments while highlighting practical integration challenges and performance trade-offs.
Entangled-photon sources are indispensable components in free-space quantum key distribution (QKD) systems. Here, we present a compact, lightweight, and robust airborne entangled-photon source (AEPS) based on a Sagnac loop structure with single-mode fiber coupling. To meet the drone requirements for miniaturization, lightweight design, and high robustness, we developed a highly integrated entangled-photon source using customized miniature optical components and an adhesive bonding technique. The total volume and weight are only 38 × 40 × 24 mm3 and 58 g, respectively. Entangled-photon pairs at 810 nm are generated via Type-II spontaneous parametric down-conversion (SPDC) in a periodically poled KTiOPO4 (PPKTP) crystal. We achieve a quantum state fidelity of F = 0.986 ± 0.0017, a photon-pair generation rate of 3.03 × 106 pairs/s/mW, and a CHSH Bell parameter of S = 2.764 ± 0.082. Owing to its excellent size, weight, performance, and stability, the proposed entangled-photon source is particularly well suited for drone-based free-space mobile quantum communication.
Fiber-based quantum communication networks are currently limited without quantum repeaters. Satellite-based quantum links have been proposed to extend the network domain. We develop a quantum communication system, suitable for realistic satellite-to-ground communication. With this system, we execute an entanglement-based quantum key distribution (QKD) protocol developed by Bennett, Brassard, and Mermin (BBM92), achieving quantum bit-error rates (QBERs) below 2% in all bases. More importantly, we demonstrate low-QBER execution of a higher-dimensional hyperentanglement-based QKD protocol, using photons simultaneously entangled in polarization and time bin, leading to significantly higher secure key rates, at the cost of increased technical complexity and system size. We show that our protocol is suitable for a space-to-ground link, after incorporating Doppler-shift compensation, and verify its security using a rigorous finite-key analysis. Additionally, we discuss system-engineering considerations relevant to those and other quantum communication protocols and their dependence on what photonic degrees of freedom are utilized.
Unmanned Aerial Vehicles (UAVs) are used in numerous applications ranging from defense, law enforcement, environmental monitoring, disaster recovery, aerial photography, and delivering consumer packages. Securing wireless communication between drones in-flight is critical to ensure safe operation during flight and avoid multiple types of attacks, e.g., eavesdropping, spoofing, jamming, etc. Quantum communication protocols offer enhancements over classical approaches. In this effort, we present progress towards demonstrating Quantum Key Distribution (QKD) between two drones in flight. A significant challenge includes achieving system performance using compact Size, Weight, and Power (SWaP) constraints of the drone vehicle. We introduce and evaluate critical subsystems including the QKD source, which is based on resonant-cavity Light Emitting Diodes (LED) controlled by an FPGA, and we discuss a secondary QKD source based on a fiber-coupled polarization modulator. The Pointing, Acquisition and Tracking (PAT) system is comprised of several cascading subsystems, which provide course alignment using based on Infrared (IR) beacons/cameras with gimbals, and fine alignment using Fast Steering Mirrors (FSM) with absolute encoders and feedback position sensors. We discuss both transmit and receive optics including custom designed 3D-printed optical benches. Finally, we introduce single-photon detectors, FPGA-based time-tagger, and a novel statistical post-processing synchronization algorithm. Establishing a quantum communications link between drones in-flight is an important prerequisite for future drone-based quantum applications such as entanglement distribution, distributed quantum sensing, and Quantum Positional Verification (QPV).
Abstract Quantum key distribution (QKD) is believed to represent a viable solution to achieve theoretically unconditionally secure key generation. However, the available optical systems for experimental QKD, based on photon transmission, are flawed by non-idealities that ultimately limit the achievable performance. Classical simulation of the optical hardware employed in these systems may take on a determining role in engineering future QKD networks. In this article, attempts for developing a QKD simulator based on low-computational-cost models of the employed hardware are presented. In particular, the simulation infrastructure targets polarization-based QKD setups with faint laser sources, whose behaviour can be described by semiclassical coherent states and Mean Photon Number (MPN) per beam. The effects of passive optical components on the photonic qubit evolution are described by Jones matrices, whose coefficients, for some commercial devices, are stored in anad-hoclibrary. Realistic eavesdropping attacks and non-idealities, such as optical losses, fibre attenuation, polarization misalignment and limited efficiency of single-photon detectors, are also taken into account. The infrastructure allows the user to describe the desired QKD configuration and it provides in output the MPN at the receiver and two fiducial performance parameters: Quantum Bit Error Rate (QBER) and secure key rate. The comparison of the simulation results with experimental data in the state-of-the-art literature highlights that this work is a step forward towards the definition of compact models for the hardware-dependent simulation of quantum-assisted communication networks.