,
Frédéric Magniez
,
Sayantan Sen
,
Dániel Szabó
Creative Commons Attribution 4.0 International license
We initiate the study of quantum property testing in sparse directed graphs, and more particularly in the unidirectional model, where the algorithm is allowed to query only the outgoing edges of a vertex. In the classical unidirectional model, the problem of testing k-star-freeness, and more generally k-source-subgraph-freeness, is almost maximally hard for large k. We prove that this problem has almost quadratic advantage in the quantum setting. Moreover, we show that this advantage is nearly tight, by showing a quantum lower bound using the method of dual polynomials on an intermediate problem for a new, property testing version of the k-collision problem that was not studied before. To illustrate that not all problems in graph property testing admit such a quantum speedup, we consider the problem of 3-colorability in the related undirected bounded-degree model, when graphs are now undirected. This problem is maximally hard to test classically, and we show that also quantumly it requires a linear number of queries.
@InProceedings{apers_et_al:LIPIcs.APPROX/RANDOM.2025.32,
author = {Apers, Simon and Magniez, Fr\'{e}d\'{e}ric and Sen, Sayantan and Szab\'{o}, D\'{a}niel},
title = {{Quantum Property Testing in Sparse Directed Graphs}},
booktitle = {Approximation, Randomization, and Combinatorial Optimization. Algorithms and Techniques (APPROX/RANDOM 2025)},
pages = {32:1--32:24},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-397-3},
ISSN = {1868-8969},
year = {2025},
volume = {353},
editor = {Ene, Alina and Chattopadhyay, Eshan},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.APPROX/RANDOM.2025.32},
URN = {urn:nbn:de:0030-drops-243987},
doi = {10.4230/LIPIcs.APPROX/RANDOM.2025.32},
annote = {Keywords: property testing, quantum computing, bounded-degree directed graphs, dual polynomial method, collision finding}
}