⚛️ quantum physics

Drone- and Vehicle-Based Quantum Key Distribution

This paper presents a modular, mobile quantum key distribution system deployed on drones and vehicles that achieves secure key rates of 1.6–20 kbps by utilizing advanced physics models to address non-ideal behaviors in dynamic environments.

Original authors: Andrew Conrad, Roderick Cochran, Daniel Sanchez-Rosales, Samantha Isaac, Timur Javid, Tahereh Rezaei, A. J. Schroeder, Grzegorz Golba, Akash Gutha, Brian Wilens, Kyle Herndon, Alex Hill, Joseph Chapma

Published 2026-08-25

📖 6 min read🧠 Deep dive

CC BY 4.0

Original authors: Andrew Conrad, Roderick Cochran, Daniel Sanchez-Rosales, Samantha Isaac, Timur Javid, Tahereh Rezaei, A. J. Schroeder, Grzegorz Golba, Akash Gutha, Brian Wilens, Kyle Herndon, Alex Hill, Joseph Chapman, Ian Call, Joseph Szabo, Aodhan Corrigan, Lars Kamin, Norbert Lütkenhaus, Daniel J. Gauthier, Paul G. Kwiat

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine a world where the very laws of physics, rather than complex mathematical codes, guarantee that a secret message cannot be intercepted. This is the promise of quantum key distribution, a method of sending information that relies on the behavior of individual particles of light. In this system, the sender and receiver share a secret code by exchanging these tiny particles. If a third party tries to spy on the exchange, the act of looking at the particles inevitably changes them, alerting the two honest parties that the line is compromised. For years, this technology has been confined to fixed locations, connected by fiber-optic cables or short, stationary beams of light. The challenge has always been to take this delicate, high-security technology out of the lab and put it on the move, allowing it to work between objects that are flying or driving.

A team of researchers has now successfully demonstrated that this is possible. They built a portable system capable of generating secure keys between moving platforms, including drones and vehicles. By mounting their equipment on commercial drones and cars, they proved that two parties can exchange a secret code while in motion, whether they are hovering in the air, driving side-by-side on a test track, or speeding along a public highway. The system worked even when the vehicles were traveling at speeds of up to 70 miles per hour, generating a secure code that could be used to encrypt future communications. This achievement moves quantum security from a static laboratory experiment toward a flexible network that could one day protect data for mobile users anywhere.

The core of this project was a modular design, meaning the quantum equipment could be quickly swapped between different vehicles without needing to be rebuilt from scratch. The researchers constructed a transmitter and a receiver that were small and light enough to be carried by drones, yet powerful enough to maintain a connection over distance. The transmitter sends out pulses of light encoded with information, while the receiver measures them. To keep the connection stable while the platforms moved, the team used a pointing and tracking system. This system acts like a steady hand, constantly adjusting the aim of the laser to ensure the beam stays locked onto the receiver despite the vibrations and movements of the drones and cars.

The team tested their system in several different scenarios to see how well it held up under real-world conditions. First, they tested the equipment on the ground, with the transmitter and receiver sitting on stationary drones separated by a short distance. Then, they took to the air, flying two drones toward each other and maintaining a secure link while hovering about 13 feet apart. They also tested a scenario where a flying drone communicated with a car driving on a private road. Finally, they pushed the system to its limits by placing the equipment in two cars driving parallel to each other. In one test, the cars moved slowly at 5 miles per hour on a closed track. In a more demanding test, they drove side-by-side at 70 miles per hour on a public interstate highway.

In every configuration, the system successfully generated a secret key. The speed at which they could generate this key varied depending on the conditions. When the cars were moving slowly, the system produced a secure key at a rate of 20 kilobits per second. Even at the high speed of 70 miles per hour on the interstate, the system maintained a connection, generating a key at a rate of 2.5 kilobits per second. The drone-to-drone connection achieved a rate of 8.5 kilobits per second, while the drone-to-vehicle link produced 1.6 kilobits per second. These numbers represent the speed at which the two parties could agree on a secret code that was mathematically proven to be secure against eavesdropping.

A critical part of this success was how the researchers handled the imperfections of the real world. In a perfect laboratory, equipment works flawlessly, but on a moving vehicle, vibrations, changing light, and mechanical shifts cause errors. The team developed a new way of analyzing the data that accounted for these flaws. Instead of assuming the equipment was perfect, they built a detailed model of how their specific devices behaved, including how the detectors missed some signals or how the light beams shifted. By using this realistic model, they could prove that the system remained secure even with these errors, a crucial step for any technology intended for mobile use. This approach allowed them to calculate a secure key rate that was trustworthy, even though the sessions were relatively short.

The researchers also noted the limitations of their current setup. The system currently operates only at night because sunlight creates too much background noise for the sensitive detectors to distinguish the signal. They believe that with better filters and more advanced equipment, they could eventually make the system work during the day. Additionally, the drones they used were limited by battery life, allowing for only a few minutes of flight time, which restricted how far they could travel. The team suggested that using a tether to supply power to the drone, or using larger military-grade drones, could extend the range and duration of these flights. They also pointed out that their current system has a range of about 100 meters, but future upgrades with more powerful lasers could extend this to 15 kilometers.

This work represents a significant step toward a future where quantum communication is not limited to fixed buildings or cables. By proving that secure keys can be exchanged between moving platforms, the researchers have laid the groundwork for a dynamic quantum network. In such a network, vehicles, drones, and other mobile devices could establish secure connections on the fly, exchange keys, and then separate to use those keys for long-distance, encrypted communication. The ability to swap the equipment between different platforms in less than an hour suggests that this technology could be adapted for various needs, from military applications to secure logistics. While the system is not yet ready for widespread commercial use, the demonstration shows that the physics of quantum security can survive the turbulence of the real world.

Technical Summary: Drone- and Vehicle-Based Quantum Key Distribution

Problem Statement

The development of a global quantum internet requires the ability to interface quantum computers and sensor networks via reconfigurable, mobile nodes. While proof-of-concept quantum networks have been demonstrated using fixed ground stations, metropolitan-scale entanglement, and space-to-ground links, a significant challenge remains: demonstrating secure quantum communication between fully mobile platforms "on-the-go," such as drones and vehicles.

Existing mobile Quantum Key Distribution (QKD) demonstrations have largely relied on simplified security analyses that assume idealized equipment and infinitely long exchange sessions. These assumptions are invalid for mobile platforms, where communication sessions are brief, and device non-idealities (such as vibrations, alignment drifts, and varying transmission efficiencies) are pronounced. There is a critical need for a modular, platform-agnostic QKD system that can operate between moving nodes while providing rigorous security proofs that account for finite-key regimes and real-world hardware imperfections.

Methodology

System Architecture

The authors developed a modular, platform-agnostic QKD transmitter and receiver system designed for reduced Size, Weight, and Power (SWaP). The system utilizes a polarization-based protocol (BB84 with decoy states) and includes a Pointing-and-Tracking (PAT) system to maintain the optical link between moving platforms.

Modularity: The QKD payload is designed to be swapped between different mobile platforms (drones and vehicles) in under an hour.
Protocol: The system encodes information using circular polarization states ( $|R\rangle$ and $|L\rangle$ ) for key generation and horizontal polarization ( $|H\rangle$ ) for error checking. It employs attenuated LEDs as sources, utilizing three intensity levels (signal, decoy, and vacuum) to prevent photon-number splitting attacks.
Hardware: The setup includes single-photon counting detectors, time taggers, and post-processing units. The drone platform used is a commercial octocopter (Freefly Systems Alta 8 Pro) with a payload capacity of ~9 kg.

Experimental Configurations

The system was deployed and tested in six distinct configurations to evaluate performance across varying mobility and environmental conditions:

Tabletop: Stationary baseline.
Ground-to-Ground: Stationary drones separated by 10 m.
Drone-to-Drone (Air-to-Air): Two drones hovering at ~4 m altitude, separated by ~10 m.
Drone-to-Vehicle (Air-to-Vehicle): A drone flying parallel to a ground vehicle at ~10 mph.
Vehicle-to-Vehicle (Slow): Two vehicles traveling parallel at 5 mph on a closed test track.
Vehicle-to-Vehicle (High-Speed): Two vehicles traveling parallel at 70 mph on a U.S. Interstate Highway.

Security Analysis

A primary methodological contribution is the development of an advanced security analysis tailored for mobile platforms. Unlike previous works that assume ideal devices, this analysis:

Finite-Key Regime: Calculates secure key rates for short, finite-duration sessions typical of mobile encounters.
Device Modeling: Incorporates detailed physics models of non-ideal behaviors, including variable link transmission, mismatched detector efficiencies, and state-dependent detection rates.
Adversarial Model: Assumes a collective attack by an eavesdropper (Eve) and uses a composable $\epsilon$ -security framework. The analysis treats all losses and imperfections as potentially attributable to the eavesdropper, ensuring a conservative and robust security statement.

Key Results

The system successfully generated secure keys in all tested configurations, achieving secret key rates in the finite-key regime ranging from 1.6 kbps to 20.0 kbps.

Drone-to-Drone: Achieved a secure key rate of 8.5 kbps with a total secret key of 1.4 Mb over a 166.4-second flight. The count rates showed periodic drops due to the transmitter's duty cycle for data saving and time synchronization.
Drone-to-Vehicle: Achieved a secure key rate of 1.6 kbps (total 204.5 kb) over an 806 m path. The transmission was stable, though the relative proportion of the right-circular polarization count rate was lower than expected, a factor successfully accounted for in the custom security model.
Vehicle-to-Vehicle (5 mph): Achieved the highest secure key rate of 20.0 kbps with a total key of 1.88 Mb. The quantum transmission was notably more stable than in drone experiments due to lower vibration intensity.
Vehicle-to-Vehicle (70 mph): Achieved a secure key rate of 2.5 kbps (total 519 kb) on a public highway. This required modifications to the pointing laser beacons to operate at eye-safety levels.

In all cases, the system produced a secure key using only a single flight or drive session, demonstrating the feasibility of "on-the-fly" key exchange.

Significance and Claims

The paper claims several significant contributions to the field of quantum networking:

First Fully Mobile QKD Links: This work demonstrates the first QKD links between fully mobile platforms in all three configurations: drone-to-drone, drone-to-vehicle, and vehicle-to-vehicle.
Rigorous Finite-Key Security: The authors assert that their advanced security analysis, which accounts for specific non-idealities of mobile hardware and operates in the finite-key regime, provides a more realistic and robust security proof than previous simplified models.
Modularity and Reconfigurability: The system proves that quantum communication payloads can be rapidly deployed and swapped between heterogeneous platforms (drones and cars), a prerequisite for dynamic, reconfigurable quantum networks.
Stepping Stone to Entanglement: While the current demonstration uses weak coherent pulses (not entangled states), the authors state that the system design and supporting hardware (pointing, synchronization, detection) are identical to those required for entanglement-based protocols. Thus, this work serves as a foundational step toward a mobile, entanglement-based quantum internet.
Practicality of Free-Space QKD: The results validate that free-space QKD is practical for moving platforms, even under high-speed conditions and with brief interaction times, provided that non-idealities are properly modeled.

The authors acknowledge current limitations, including night-only operation (due to background noise), a PAT range of roughly 100 m, and battery constraints for drones. However, they outline a clear path for future upgrades, such as improved filtering for daylight operation and higher-power beacons for longer-range links, suggesting that the technology is scalable for future heterogeneous quantum networks.