Given a Boolean function f : {0,1}ⁿ → {0,1}, the goal in the usual query model is to compute f on an unknown input x ∈ {0,1}ⁿ while minimizing the number of queries to x. One can also consider a "distinguishing" problem denoted by f_sab: given an input x ∈ f^{-1}(0) and an input y ∈ f^{-1}(1), either all differing bits are replaced by a *, or all differing bits are replaced by †, and an algorithm’s goal is to identify which of these is the case while minimizing the number of queries. Ben-David and Kothari [ToC'18] introduced the notion of randomized sabotage complexity of a Boolean function to be the zero-error randomized query complexity of f_sab. A natural follow-up question is to understand the 𝖰(f_sab), the quantum query complexity of f_sab. In this paper, we initiate a systematic study of this. The following are our main results for all Boolean functions f : {0,1}ⁿ → {0,1}. - If we have additional query access to x and y, then 𝖰(f_sab) = O(min{𝖰(f),√n}). - If an algorithm is also required to output a differing index of a 0-input and a 1-input, then 𝖰(f_sab) = O(min{𝖰(f)^{1.5}, √n}). - 𝖰(f_sab) = Ω(√{fbs(f)}), where fbs(f) denotes the fractional block sensitivity of f. By known results, along with the results in the previous bullets, this implies that 𝖰(f_sab) is polynomially related to 𝖰(f). - The bound above is easily seen to be tight for standard functions such as And, Or, Majority and Parity. We show that when f is the Indexing function, 𝖰(f_sab) = Θ(fbs(f)), ruling out the possibility that 𝖰(f_sab) = Θ(√{fbs(f)}) for all f.
@InProceedings{cornelissen_et_al:LIPIcs.FSTTCS.2024.19, author = {Cornelissen, Arjan and Mande, Nikhil S. and Patro, Subhasree}, title = {{Quantum Sabotage Complexity}}, booktitle = {44th IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2024)}, pages = {19:1--19:20}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-355-3}, ISSN = {1868-8969}, year = {2024}, volume = {323}, editor = {Barman, Siddharth and Lasota, S{\l}awomir}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FSTTCS.2024.19}, URN = {urn:nbn:de:0030-drops-222082}, doi = {10.4230/LIPIcs.FSTTCS.2024.19}, annote = {Keywords: Sabotage complexity, quantum query complexity, Boolean functions, fractional block sensitivity} }
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