KEYWORDS: Satellites, Quantum key distribution, Quantum modeling, Systems modeling, Satellite communications, Quantum bit errors, Quantum protocols, Free space optical communications, Quantum based satellite communication, Satellite to ground quantum key distribution
Quantum Key Distribution (QKD) is a potential mitigation against quantum computation advances that threaten currently deployed public key cryptosystems. QKD is also a precursor to large-scale quantum communications and the quantum internet. Terrestrial direct transmission of quantum photonic signals is restricted by optical fibre exponential absorption, hence space-based systems have been proposed for intercontinental distribution of quantum keys with lower-loss free-space transmission through vacuum. However, challenges remain for the practical deployment of satellite QKD (SatQKD) such as weather, background light, and terminal deployment. In particular, the short transmission time inherent in low Earth orbit satellite QKD and finite statistical uncertainty can limit secure key generation. Here we illustrate the analysis of these effects and some practical engineering design and operational constraints on key length using the Satellite Quantum Modelling and Analysis (SatQuMA) software package being developed for satellite quantum communications research.
Quantum enhanced receivers are endowed with resources to achieve higher sensitivities than conventional technologies. For application in optical communications, they provide improved discriminatory capabilities for multiple non-orthogonal quantum states. In this work, we propose and experimentally demonstrate a new decoding scheme for quadrature phase-shift encoded signals. Our receiver surpasses the standard quantum limit and outperforms all previously known non-adaptive detectors at low input powers. Unlike existing approaches, the receiver only exploits linear optical elements and on-off photo-detection. This circumvents the requirement for challenging feed-forward operations that limit communication transmission rates and can be readily implemented with current technology.
Developing global quantum communication networks is integral to the realisation of the quantum internet, which
is expected to impart a similar revolutionary impact on the technological landscape as the classical internet.
Satellite-based quantum communications provides a practical route to global quantum networking. In this work,
we model finite statistics to determine the finite secret key length generation in SatQKD systems that implement
trusted-node downlink operation with weak coherent pulse sources. We optimise the finite key rate for different
practical operations and determine the key generation footprints. Our work provides an essential guide for future
satellite missions to establish performance benchmarks for both sources and detectors.
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