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Controlled quantum search

  • 01-10-2018
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Abstract

Quantum searching for one of N marked items in an unsorted database of n items is solved in \(\mathcal {O}(\sqrt{n/N})\) steps using Grover’s algorithm. Using nonlinear quantum dynamics with a Gross–Pitaevskii-type quadratic nonlinearity, Childs and Young (Phys Rev A 93:022314, 2016, https://doi.org/10.1103/PhysRevA.93.022314) discovered an unstructured quantum search algorithm with a complexity \(\mathcal {O}( \min \{ 1/g \, \log (g n), \sqrt{n} \}) \), which can be used to find a marked item after \(o(\log (n))\) repetitions, where g is the nonlinearity strength. In this work we develop an quantum search on a complete graph using a time-dependent nonlinearity which obtains one of the N marked items with certainty. The protocol has runtime \(\mathcal {O}(n /(g \sqrt{N(n-N)}))\), where g is related to the time-dependent nonlinearity. We also extend the analysis to a quantum search on general symmetric graphs and can greatly simplify the resulting equations when the graph diameter is less than 4.

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Title
Controlled quantum search
Authors
K. de Lacy
L. Noakes
J. Twamley
J. B. Wang
Publication date
01-10-2018
Publisher
Springer US
Published in
Quantum Information Processing / Issue 10/2018
Print ISSN: 1570-0755
Electronic ISSN: 1573-1332
DOI
https://doi.org/10.1007/s11128-018-2031-6
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