Space Quantum Communication

The distortion of photons propagation in a curved spacetime geometry poses a challenge for communication for Earth-to-satellite communication. Here, the distortion of localized information carriers, arising from curved spacetime geometry, as they are freely transported along a general geodesic is reported.

As quantum communication networks mature and expand to global scale, free-space links will become increasingly important in bridging the distances involved. The authors provide a model for such links under conditions in which atmospheric turbulence is significant, showing that a finite key rate is possible even in challenging scenarios such as satellite operating at high zenith angle.

In scaling to global distances, future quantum networks are expected to make use of satellite-based orbiting quantum memories. In this manuscript, the authors simulate the performance of memory-assisted quantum key distribution (MA-QKD) schemes under a range of operating conditions and network configurations, with encouraging conclusions as to the feasibility of implementing such networks with near-term devices.

This study confirms that a classical channel model can be used for describing random fluctuations in LEO-to-ground quantum atmospheric channels. It shows that practical engineering designs for future QKD missions can be conveniently conducted using the verified channel model, and that deep learning can predict channel fluctuations.

Quantum Random Number Generators (QRNG) are important components of cryptographic protocols including prepare-and-measure based quantum key distribution protocols. The authors demonstrate laboratory, as well as in-orbit operation of their QRNG, showing its use to implement a public randomness beacon.

The first generation of global-scale quantum networks are expected to make extensive use of satellite-mediated channels. As a first step towards this goal, this manuscript proposes a full-scale architecture to implement the exchange of quantum information, taking us from use cases through to a detailed plan for the road ahead.

Finite key analysis is the gold standard in evaluating the performance of satellite-based quantum key distribution (SatQKD) but implementing a fully optimised parameter space is challenging. The authors present practical performance limits to SatQKD that account for engineering limitations and mission design trade-offs, providing valuable insight for the next generation of satellite-based missions.