Paper Abstract and Keywords |
Presentation |
2012-04-27 10:35
Reconstructing Strings from Substrings with Quantum Queries Richard Cleve (Univ. of Waterloo), Kazuo Iwama (Kyoto Univ.), Francois Le Gall (Univ. of Tokyo), Harumichi Nishimura (Nagoya Univ.), Seiichiro Tani (NTT), Junichi Teruyama (Kyoto Univ.), Shigeru Yamashita (Ritsumeikan Univ.) COMP2012-2 |
Abstract |
(in Japanese) |
(See Japanese page) |
(in English) |
This paper investigates the number of quantum queries made
to solve the problem of reconstructing an unknown string from its
substrings in a certain query model. More concretely, the goal of the problem is
to identify an unknown string $S$ by making queries of the following
form: ``Is $s$ a substring of $S$?'', where $s$ is a query string over the given alphabet.
The number of queries required to identify the string $S$ is the query complexity of this problem.
First we show a quantum algorithm that exactly identifies the string $S$
with at most $\frac{3}{4}N + o(N)$ queries, where $N$ is the length of $S$.
This contrasts sharply with the classical query complexity~$N$.
Our algorithm uses Skiena and Sundaram's classical algorithm
and the Grover search as subroutines.
To make them effectively work, we develop another subroutine
that finds a string appearing only once in $S$, which may have an
independent interest. We also prove that any bounded-error quantum algorithm
needs $\Omega(\frac{N}{\log^2{N}})$ queries.
For this, we introduce another query model and obtain a lower bound
for this model with the adversary method, from which bound
we get the desired lower bound in the original query model. |
Keyword |
(in Japanese) |
(See Japanese page) |
(in English) |
quantum computing / string algorithms / query complexity / lower bounds / / / / |
Reference Info. |
IEICE Tech. Rep., vol. 112, no. 21, COMP2012-2, pp. 7-14, April 2012. |
Paper # |
COMP2012-2 |
Date of Issue |
2012-04-20 (COMP) |
ISSN |
Print edition: ISSN 0913-5685 Online edition: ISSN 2432-6380 |
Copyright and reproduction |
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