Quantum Drones – Better than Owls
Battle of the Owl Metaphors
Recently, I was struck by a battle of Owl Metaphors, overlaid on top of real-life battles.
Owls, as fierce, nocturnal predators, have wide wings, light bodies, and feathers specially-designed to allow them to silently swoop down on prey including on bats. Drones, or unmanned aerial vehicles (UAV), are the perfect nonliving successor to small, silent, air maneuvers. In todays’ real-life battles, biomimicry is one drone frontier to use drone body shape to ‘hide in plain sight’.
This owl-shaped drone in Fig. 1, resembling a Snowy Owl, does just that. Its technological improvements are quieter air flight and a laser to illuminate targets. Its navigation system is dependent upon the GLONASS satellite system, however, which needs a renewal in the next few years of its aged satellites. Moreover, such drones, whether position-dependent on GLONASS or its American version: GPS, often experience jammed satellite signals in conflict zones.
Signal jamming is a given in any conflict zone, including in Ukraine, which is why the most sophisticated drones include digital signal encryption. Which cryptographic standard? Today, the drone encryption standard is typically AES, which is at risk in the quantum computing era.
Enter: Quantum Drones
Free-space Quantum Key Distribution (QKD) allows two parties to share a random key with unconditional security, between ground stations, between mobile platforms, and even in satellite-ground quantum communications. Drones have a variety of advantages: quick deployment, cost-effectiveness, and an ability to provide quantum connections at different altitudes from a local-area to broad-area scales.
Are drones able to transmit and receive quantum-encrypted data yet? Yes and No. Extra QKD preparation is required at the drones and at the nodes, as the following experiment demonstrates.
A Stopgap for Wireless Quantum Key Distribution (QKD)
Villages located in regions, where aggressive neighbors can eavesdrop or impede electronic communication, are in need of a way to transmit secure information. The South Korean Gangwon-do province presented such an opportunity, because its northern boundary is the Military Demarcation Line, separating it from North Korea’s Kangwon Province.
The Gangwon-do quantum drone program became a successful Quantum Key Distribution Network (QKDN) Use Case for South Korea’s KT Corporation, to securely transmit video drone data between two adjacent local governments. See Fig. 2.
KT’s Dr. Hyung-Soo (Hans) Kim presented an outline of his company’s successful quantum drone QKDN at the February 2022 IQT Hague meeting. He elaborated further on its operational process in email.
The wireless communication provides connectivity between the drone and the local government’s monitoring center. A set of QKD systems “Alice” and “Bob”, for example at “Local governments” A and B (Fig. 2), is installed at both ends of the leased-line, to provide the QKD-based security (quantum cryptography) into the optical cable. However, the drone is located out of sight of QKD connectivity.
By injecting the quantum encryption key supplied from QKD into the encryptors of the Control center — Local government B in Fig. 2, and the drone — prior to flying, not only is the drone control, signal-protected, but also the video signal from the drone is encrypted and protected. From this point-of-view, the center and the drone (during flying) can communicate with QKD-encrypted data.
Wireless QKD technologies have not been commercially implemented yet, as it is challenging for mobile objects to perform with the required high-accuracy pointing and tracking. Atmospheric turbulence causes fluctuations in transmittance, which further affect the quantum bit error rate (QBER) and the secure key rate. This is a stopgap solution for mobile object security before full wireless QKD technology is realized.
QKD with Two Drones, all COTS
What about QKD Drone-to-Drone? That QKD drone system is in development too. A team led by University of Illinois PhD candidate Andrew Conrad presented the specifications for a Two-Drone, QKD system, using commercial off-the-shelf (COTS) parts, ‘Drone-based quantum key distribution (QKD)‘, March 5, 2021, published online by SPIE. The specifications can be seen in detail in an excellent 25-minute video at QCrypt 2021 here. As Conrad is in the post-preliminary PhD phase, I hope to report on the construction of this QKD drone demonstration in the future.
Quantum Entanglement with Two Drones
With a shift to end-to-end, quantum drone communication, we’ll move to the successful demonstration of the first quantum link between two mobile platforms by H. -Y. Liu X. -H. Tian and colleagues from China’s Nanjing University in their research published in Phys. Rev. Lett. in January 2021
Liu et al, 2021, identify the two key technological developments for their achievement (see the paper’s Figure 2)
- the airborne entangled photon source (AEPS), and
- their acquisition, pointing, and tracking (APT) system (sometimes referred by others as Pointing, Acquisition and Tracking — PAT— system).
Figure 3. A quantum communication system which consists of Drone 1 (left) that generates entangled photon pairs and distributes them to ground stations: “Alice” and “Bob”. One photon (purple beam) goes directly to the ground, while the other drone: Drone 2, collects photons from Drone 1 (pink beam), and serves as a relay node. The distance between Alice and Bob ground stations exceeds 1 km. Provided by X. -H. Tian, H. -Y. Liu, & Z. Xie/Nanjing University.
The AEPS carried by Drone 1, generates the single-photon beam: entangled photons, which are directed toward Drone 2, the relay node. Drone 2 carries a transceiver unit that includes a telescope for coarse tracking to image the 940 nm light diode from Drone 1. The transceiver couples the light into the Single Mode Fiber (SMF), which is an optical fiber that is designed to carry only a single, transverse light mode. Eventually, the light is collimated toward the destination or the next node. The entangled photons are then distributed to the ground, Alice and Bob stations, which are 1 km apart with an optical relay. One drone’s payload weight is 11.8 kg; a total takeoff weight with the drone is 35 kg. A further weight reduction is possible using more custom components.
Quantum Drones All the Way Down
As other researchers have demonstrated Free-space QKD from:
then, readers here would be correct in their conclusion that Quantum Drones are beginning to fly in our imagination. For example, a look to Google Patents shows a surprising 2000 granted patents on the topic of Quantum Drones.
The Big Picture view of quantum drones in free space quantum technology shows quantum drones’ role in our future from the large application to the small. See Fig. 4. To inspire our imaginations, Kumar et at, 2022, in a May 2022 preprint in Vehicular Communications titled: “Futuristic view of the Internet of Quantum Drones” explores the potential applications of these drone-related futuristic disruptive technologies for social concerns. Today, quantum drones are ‘hiding in plain sight’.
Figure 4. A possible scenario of how the Internet of Quantum Devices (IoQDs) and the constellation of satellites can be formulated and integrated with ground networks for various applications in the May 2022 preprint by Kumar et al., 2022.
Amara is an interdisciplinary physicist, planetary scientist, science communicator and educator and expert on all quantum technologies.