Single-Satellite Quantum Repeater Performance Analysis

TL;DR

This paper compares the performance of direct dual downlink entanglement distribution and single-satellite quantum repeaters for space-based quantum communication, analyzing various operational and geometric factors.

Contribution

It provides a detailed performance analysis of a single-satellite quantum repeater versus direct distribution, informing future space quantum network designs.

Findings

Direct dual downlink can bypass classical communication latency constraints.

Performance depends on overpass geometry and ground station altitudes.

Quantum memory and decoherence significantly affect entanglement fidelity.

Abstract

Space-based entanglement distribution has the potential to extend the range of quantum communication beyond that achievable through optical fibres that are constrained by exponential losses. Quantum repeaters have been proposed to mitigate the effects of channel losses for both fibre and satellite networks. Although quantum repeaters can improve entanglement distribution efficiency, the rate is constrained by classical communication latency in the entanglement swapping process. Direct dual downlink entangled pair distribution does not suffer such a latency restriction, hence can ``brute force'' the problem of high dual channel loss through increased source rate. Hence, the comparative requirements of direct pair distribution versus quantum repeater satellites are important for the design and deployment of space-based entanglement distribution systems. Here, we consider the simplest case of a single satellite establishing entanglement between two ground stations, comparing the performance of direct dual downlink to that of a space-based quantum repeater for general overpass geometries. We also study the long-term entanglement distribution performance for different ground station pairs and determine altitudinal dependence. Finally, we study the fidelity distribution of a satellite repeater system through Monte Carlo modelling of waiting times and rate statistics, exploring the effect of quantum memory capacity, decoherence rates, and operational policies. These results will inform mission design for future space-borne quantum repeater nodes, as well as requirements on space-based memory platforms.