Theory of Computing
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Title : Upper Bounds on Quantum Query Complexity Inspired by the Elitzur--Vaidman Bomb Tester
Authors : Cedric Yen-Yu Lin and Han-Hsuan Lin
Volume : 12
Number : 18
Pages : 1-35
URL : http://www.theoryofcomputing.org/articles/v012a018
Abstract
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Inspired by the Elitzur--Vaidman bomb testing problem (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 derive upper bounds on quantum query
complexity: we give a method of finding bomb query algorithms from
classical algorithms, which then provide non-constructive upper bounds
on $Q(f)=\Theta(\sqrt{B(f)})$. Subsequently, we were able to give
explicit quantum algorithms matching our new bounds. We apply this
method to 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 $O(n^{1.5}\log n)$
(Durr et al. 2006, Furrow 2008). Applying this method to the maximum
bipartite matching problem gives an algorithm with $O(n^{1.75})$
quantum query complexity, improving the best known (trivial) $O(n^2)$
upper bound.
A conference version of this paper appeared in the Proceedings of the
30th Computational Complexity Conference, 2015.
DOI: 10.4230/LIPIcs.CCC.2015.537