QNETSIM for memory assisted design of satellite and hybrid quantum networks

Abstract

Space-based quantum information networks require simulation tools that capture orbital dynamics, probabilistic quantum operations, and classical coordination. We introduce QNETSIM, a modular discrete-event simulator for the design and performance evaluation of satellite and hybrid space-ground quantum networks. The framework integrates orbital geometry, free-space optical and fiber channels, quantum memories, entanglement generation, and Bell-state measurements within a common event-driven architecture. Physical models account for optical loss, atmospheric turbulence, detector imperfections, finite memory capacity, and storage-induced decoherence. Space-time routing and segmented nesting support entanglement distribution across changing topologies, while a software-defined control plane coordinates generation, storage, and swapping. Configurable scenarios encompass onboard repeaters, satellite constellations, ground-based repeaters, and direct satellite distribution. Through explicit interfaces between physical models, network protocols, and orchestration, QNETSIM links component characteristics and operational policies to entanglement fidelity, throughput, latency, availability, and memory utilization, enabling systematic exploration of architectural and resource-management trade-offs in future space-based quantum information networks.

QNETSIM addresses how orbital motion, probabilistic entanglement operations, finite quantum memories, and classical coordination jointly determine satellite and hybrid quantum-network performance. It introduces a modular discrete-event simulator combining orbital geometry, free-space and fiber links, memory loading and decoherence, entanglement swapping, space–time routing, and controller interfaces. Resource records preserve surviving endpoints’ original storage ages through swaps and distinguish physical completion from herald and Pauli-frame availability. The evaluation uses onboard-repeater, constellation, ground-repeater, and direct-distribution scenarios. An onboard-repeater campaign covers 32 settings with four runs each. Increasing coherence time from $T_2=30$ to $300\,\mathrm{s}$ raises integrated deliveries by only 1.36% for one co-located-terminal geometry, but by factors of 3.35 and 3.55 for two geometries with 500 km terminal separation. A separate Paris–Vienna design pass delivers 19,502 pairs over 600 s, with count-weighted conditional fidelity 0.855 and one memory bank reaching capacity. In the satellite–fiber ground-repeater scenario, approximately 7,900 deliveries meet $F\geq0.8$ for both 60 s and 600 s coherence, versus approximately 2,000 for 6 s and essentially none for 0.6 s. A direct-link calculation additionally optimizes source brightness and coincidence windows under fidelity and detector-dead-time constraints. The reported trajectories use configuration-specific reduced models; detailed Bell-vector and quantum-instrument derivations are reference formulations, not validations of those trajectories. Limitations include unspecified replication statistics for the ground-repeater plots, no demonstrated routing-policy advantage or independent-simulator/controller equivalence, assumed optical and memory parameters, and no hardware or production key-management integration validation.