Time- and Query-optimal Quantum Algorithms Based on Decision Trees
May 18, 202144 pages
Published in:
- ACM Trans.Quant.Comput. 3 (2022) 4, 19
- Published: Jul 27, 2022
e-Print:
- 2105.08309 [quant-ph]
DOI:
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Abstract: (Association for Computing Machinery)
It has recently been shown that starting with a classical query algorithm (decision tree) and a guessing algorithm that tries to predict the query answers, we can design a quantum algorithm with query complexity O(√ GT where T is the query complexity of the classical algorithm (depth of the decision tree) and G is the maximum number of wrong answers by the guessing algorithm [3, 14]. In this article, we show that, given some constraints on the classical algorithms, this quantum algorithm can be implemented in time Õ(√ GT). Our algorithm is based on non-binary span programs and their efficient implementation. We conclude that various graph-theoretic problems including bipartiteness, cycle detection, and topological sort can be solved in time O(nlogn) and with O(n) quantum queries. Moreover, finding a maximal matching can be solved with O(n) quantum queries in time O(nlogn), and maximum bipartite matching can be solved in time O(nlogn).Note:
- 44 pages
- Quantum query complexity
- quantum algorithms
- span programs
- quantum time complexity
- quantum algorithm
- topological
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