Q2NSViz: An Open-source Standalone Visualizer for Quantum Network Simulations

A decoupled, Qt-free replay engine and PyQt6 interface that turns quantum-network execution traces into navigable visual artifacts

Francesco Mazza; Marcello Caleffi; Angela Sara Cacciapuoti· 2026· DOI 10.48550/arXiv.2607.12444

The core problem

Quantum networks exhibit unique and non-classical features that make both their simulation and intuitive understanding inherently difficult. Unlike classical networks, where connectivity and state can be captured by relatively stable graph abstractions, quantum networks evolve through entanglement generation, consumption, and transformation, producing a dynamic structure that is not visible from physical topology alone. This gap between abstract protocol logic and concrete execution motivates Q2NSViz, an open-source, Python-based visualization tool for replaying and inspecting quantum-network simulation traces. The authors position Q2NSViz as a standalone companion to Q2NS, but also as a reusable component for any simulation backend that emits the same trace format. The central claim is that by turning execution traces into navigable and reproducible visual artifacts, Q2NSViz provides a zero-coding tool for researchers and educators, narrowing the distance between protocol design and observed behavior.

The primary result reported is a working open-source visualizer that reconstructs the time evolution of a simulated quantum network from execution traces. Q2NSViz exposes not only physical connectivity but also the dynamic entanglement-induced structure that is produced, consumed, and transformed by protocol execution. The reconstructed state includes physical topology, stored and in-flight qubits, classical bits and packets, measurements, and entanglement relationships. By replaying these elements over time, the tool makes visible phenomena that are otherwise buried in logs or numerical output. The authors emphasize that Q2NSViz is standalone and zero-coding for the end user, meaning researchers and educators can inspect traces without writing visualization code. It is also described as reusable by other simulation backends that emit the same trace format, which extends its value beyond the original Q2NS context. The result is therefore both a concrete software artifact and a demonstration that a decoupled trace contract can support portable, reproducible visual inspection of quantum-network simulations.

Quantum networks exhibit unique and non-classical features that make both their simulation and intuitive understanding inherently difficult. Unlike classical networks, where connectivity and state can be captured by relatively stable graph abstractions, quantum networks evolve through entanglement generation, consumption, and transformation, producing a dynamic structure that is not visible from physical topology alone. This gap between abstract protocol logic and concrete execution motivates Q2NSViz, an open-source, Python-based visualization tool for replaying and inspecting quantum-network simulation traces. The authors position Q2NSViz as a standalone companion to Q2NS, but also as a reusable component for any simulation backend that emits the same trace format. The central claim is that by turning execution traces into navigable and reproducible visual artifacts, Q2NSViz provides a zero-coding tool for researchers and educators, narrowing the distance between protocol design and observed behavior.

Q2NSViz is organized around three architectural pillars: a decoupled JSON/NDJSON trace contract, a Qt-free replay engine, and an interactive PyQt6 interface. The trace contract separates simulation output from visualization logic, so that any backend capable of emitting the agreed JSON/NDJSON records can be visualized without modifying Q2NSViz itself. The replay engine reconstructs the time evolution of the simulated network state, including physical topology, stored and in-flight qubits, classical bits and packets, measurements, and entanglement relationships. Because the replay engine is Qt-free, it can be tested, embedded, or reused independently of the graphical front end. The PyQt6 interface then provides interactive navigation over the reconstructed timeline. Conceptually, the replay can be modeled as a state-transition function over trace events:

The significance of Q2NSViz lies in its treatment of visualization as a first-class part of the simulation workflow rather than an afterthought. Quantum-network protocols are difficult to reason about because entanglement relationships form a dynamic, non-classical structure that changes as protocols execute. By reconstructing this structure over time, Q2NSViz helps close the gap between abstract protocol logic and concrete execution. The decoupled JSON/NDJSON trace contract is a notable design decision: it reduces coupling between simulator and visualizer, enables independent evolution of both, and allows third-party backends to adopt the format. The Qt-free replay engine further improves testability and reuse, while the PyQt6 interface keeps the tool accessible to non-programmers. The main limitation implied by the abstract is scope: Q2NSViz replays and inspects traces, but it does not itself simulate quantum networks, so its usefulness depends on the availability and fidelity of trace-emitting backends. Overall, Q2NSViz contributes a practical, open-source instrument for research and education, and a reusable contract that may encourage shared visualization practices across quantum-network simulation tools.

CS practitioners and researchers

Opening member content…