Terrestrial readiness campaign for space-to-ground quantum communications with a space-qualified entangled photon-pair system

TL;DR

This study demonstrates a space-to-ground quantum key distribution link using an entangled photon system on a satellite, validating the system's performance under realistic atmospheric conditions for future quantum networks.

Contribution

It provides the first operational validation of a space-ground quantum communication link with an entangled photon system on a satellite, establishing a key performance baseline.

Findings

Achieved a secret key rate of approximately 7.56 kbps.

Maintained a quantum bit error rate of 4.78%.

Validated the link budget and background rejection capabilities.

Abstract

Realizing a global quantum internet relies on the deployment of robust satellite-based entanglement distribution links. While pioneering demonstrations have established the feasibility of such links, the transition to operational infrastructure demands the validation of robust, integrated space-to-ground architectures. Here, we report on a free-space Quantum Key Distribution experiment conducted over a 1.8 km free-space link using an engineering model of the quantum payload onboard the SpeQtre satellite and the Abu Dhabi Quantum Optical Ground Station. By implementing a BBM92 protocol with polarization-entangled photons, a secret key rate of approximately 7.56 kbps with a mean quantum bit error rate of 4.78%+-0.24% was produced. The deployed system featured spectral and spatial filtering approaches identical to those in the space segment, thus validating the link budget and background rejection capabilities under realistic atmospheric conditions. These results confirm the operational compatibility between the ground and space segments, establishing a critical performance baseline for the SpeQtre mission and future space-based, large-scale quantum networks.