Airborne demonstration of a quantum key distribution receiver payload (1612.06396v2)

Abstract: Satellite-based quantum terminals are a feasible way to extend the reach of quantum communication protocols such as quantum key distribution (QKD) to the global scale. To that end, prior demonstrations have shown QKD transmissions from airborne platforms to receivers on ground, but none have shown QKD transmissions from ground to a moving aircraft, the latter scenario having simplicity and flexibility advantages for a hypothetical satellite. Here, we demonstrate QKD from a ground transmitter to a receiver prototype mounted on an airplane in flight. We have specifically designed our receiver prototype to consist of many components that are compatible with the environment and resource constraints of a satellite. Coupled with our relocatable ground station system, optical links with distances of 3-10 km were maintained and quantum signals transmitted while traversing angular rates similar to those observed of low-Earth-orbit satellites. For some passes of the aircraft over the ground station, links were established within 10 s of position data transmission, and with link times of a few minutes and received quantum bit error rates typically 3-5%, we generated secure keys up to 868 kb in length. By successfully generating secure keys over several different pass configurations, we demonstrate the viability of technology that constitutes a quantum receiver satellite payload and provide a blueprint for future satellite missions to build upon.

• The paper presents a demonstration of a quantum key distribution receiver using a reverse ground-to-air approach with a BB84 protocol and decoy states.
• The study achieved secure keys up to 868 kilobits with quantum bit error rates between 3% and 5% over link distances of 3 to 10 km.
• The research validates a receiver payload meeting space mission criteria, marking a pivotal step toward satellite-based quantum communication networks.

Airborne Demonstration of a Quantum Key Distribution Receiver Payload

This paper presents the empirical validation of quantum key distribution (QKD) between ground and airborne platforms, simulating ground-to-satellite communication. The paper showcases a QKD receiver prototype mounted on a moving aircraft, an essential step towards realizing satellite-based quantum communication networks. The research focuses on transmitting QKD signals from a ground station to an airplane, a reverse approach to the traditional downward transmission from airborne or satellite platforms. This reversed methodology carries benefits in simplicity and adaptability, particularly for satellite applications, where having the quantum source on the ground is advantageous.

The research employs a BB84 protocol in conjunction with decoy states, sending weak coherent pulses from a terrestrial source to an aircraft-mounted receiver. The pulses had a wavelength of 785 nm and were encoded with polarization states. The setup achieved quantum link distances ranging from 3 km to 10 km, with angular motion parameters matching those of low-earth-orbit (LEO) satellites. The QKD system comprised a transmitter at the ground station and a receiving apparatus on an aircraft, including a fine-pointing system, integrated optical assembly (IOA), and detector module (DM), all designed for compatibility with space mission constraints.

Strong numerical results were presented: the system maintained optical links within 10 seconds of position data transmission, with link durations of several minutes. The experiments achieved quantum bit error rates (QBER) between 3% and 5% and generated secure keys up to 868 kilobits in length across various pass configurations. For instance, during the 7 km arc pass, the system experienced a mean link loss of 48 dB, producing a secure key even after accounting for finite-size effects in relation to sample estimation errors.

The researchers emphasize the technical elements of this demonstration reflecting readiness for satellite-borne applications. The practical DM, and other custom optical components, met space-oriented criteria such as reduced mass and power consumption, robustness to mechanical and thermal stresses, and adaptability to vacuum conditions. Despite these successes, there remain challenges, like increased error rates due to atmospheric turbulence and technical limitations inherent to the demonstration, such as occasional equipment failures and configuration errors impacting initial results.

The implications of this paper are notable for the development of global-scale quantum networks. The ability to execute QKD uplinks with airborne payloads foreshadows orbital missions where satellites could function as intermediary QKD nodes. Future satellites could integrate the described receiver payload components, leveraging the practical demonstrations of pointing accuracy and secure key exchange at LEO-matched angular speeds. The research offers a concrete blueprint towards operational quantum satellite communication systems, with further investigations likely to extend the viability of entangled-based QKD protocols, alternative source configurations, and improved resilience to environmental interference.

This paper is a pivotal contribution to the fields of quantum key distribution and quantum satellite communication, presenting solid evidence of the feasibility and potential execution of a ground-to-satellite QKD network, poised to enhance secure communication infrastructure on an unprecedented scale.