We present quantum algorithms for various problems related to graph connectivity. We give simple and query-optimal algorithms for cycle detection and odd-length cycle detection (bipartiteness) using a reduction to st-connectivity. Furthermore, we show that our algorithm for cycle detection has improved performance under the promise of large circuit rank or a small number of edges. We also provide algorithms for detecting even-length cycles and for estimating the circuit rank of a graph. All of our algorithms have logarithmic space complexity.
@InProceedings{delorenzo_et_al:LIPIcs.TQC.2019.6, author = {DeLorenzo, Kai and Kimmel, Shelby and Witter, R. Teal}, title = {{Applications of the Quantum Algorithm for st-Connectivity}}, booktitle = {14th Conference on the Theory of Quantum Computation, Communication and Cryptography (TQC 2019)}, pages = {6:1--6:14}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-112-2}, ISSN = {1868-8969}, year = {2019}, volume = {135}, editor = {van Dam, Wim and Man\v{c}inska, Laura}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.TQC.2019.6}, URN = {urn:nbn:de:0030-drops-103984}, doi = {10.4230/LIPIcs.TQC.2019.6}, annote = {Keywords: graphs, algorithms, query complexity, quantum algorithms, span programs} }
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