when quoting this document, please refer to the following
URN: urn:nbn:de:0030-drops-13333

Quantum search with variable times



Since Grover's seminal work, quantum search has been studied in great detail. In the usual search problem, we have a collection of $n$ items $x_1, ldots, x_n$ and we would like to find $i: x_i=1$. We consider a new variant of this problem in which evaluating $x_i$ for different $i$ may take a different number of time steps. Let $t_i$ be the number of time steps required to evaluate $x_i$. If the numbers $t_i$ are known in advance, we give an algorithm that solves the problem in $O(sqrt{t_1^2+t_2^2+ldots+t_n^2)$ steps. This is optimal, as we also show a matching lower bound. The case, when $t_i$ are not known in advance, can be solved with a polylogarithmic overhead. We also give an application of our new search algorithm to computing read-once functions.

BibTeX - Entry

  author =	{Andris Ambainis},
  title =	{{Quantum search with variable times}},
  booktitle =	{25th International Symposium on Theoretical Aspects of Computer Science},
  pages =	{49--61},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-939897-06-4},
  ISSN =	{1868-8969},
  year =	{2008},
  volume =	{1},
  editor =	{Susanne Albers and Pascal Weil},
  publisher =	{Schloss Dagstuhl--Leibniz-Zentrum fuer Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{},
  URN =		{urn:nbn:de:0030-drops-13333},
  doi =		{},
  annote =	{Keywords: }

Seminar: 25th International Symposium on Theoretical Aspects of Computer Science
Issue date: 2008
Date of publication: 2008

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