Inspired by the Elitzur-Vaidman bomb testing problem [Elitzur/Vaidman 1993], we introduce a new query complexity model, which we call bomb query complexity B(f). We investigate its relationship with the usual quantum query complexity Q(f), and show that B(f)=Theta(Q(f)^2). This result gives a new method to upper bound the quantum query complexity: we give a method of finding bomb query algorithms from classical algorithms, which then provide nonconstructive upper bounds on Q(f)=Theta(sqrt(B(f))). We subsequently were able to give explicit quantum algorithms matching our upper bound method. We apply this method on the single-source shortest paths problem on unweighted graphs, obtaining an algorithm with O(n^(1.5)) quantum query complexity, improving the best known algorithm of O(n^(1.5) * sqrt(log(n))) [Furrow, 2008]. Applying this method to the maximum bipartite matching problem gives an O(n^(1.75)) algorithm, improving the best known trivial O(n^2) upper bound.
@InProceedings{lin_et_al:LIPIcs.CCC.2015.537, author = {Lin, Cedric Yen-Yu and Lin, Han-Hsuan}, title = {{Upper Bounds on Quantum Query Complexity Inspired by the Elitzur-Vaidman Bomb Tester}}, booktitle = {30th Conference on Computational Complexity (CCC 2015)}, pages = {537--566}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-939897-81-1}, ISSN = {1868-8969}, year = {2015}, volume = {33}, editor = {Zuckerman, David}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CCC.2015.537}, URN = {urn:nbn:de:0030-drops-50635}, doi = {10.4230/LIPIcs.CCC.2015.537}, annote = {Keywords: Quantum Algorithms, Query Complexity, Elitzur-Vaidman Bomb Tester, Adversary Method, Maximum Bipartite Matching} }
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