String Matching in ${\tilde O}(\sqrt{n}+\sqrt{m})$ Quantum Time

We show how to determine whether a given pattern p of length m occurs in a given text t of length n in ${\tilde O}(\sqrt{n}+\sqrt{m})$\footnote{${\tilde O}$ allows for logarithmic factors in m and $n/m$} time, with inverse polynomial failure probability. This algorithm combines quantum searching algorithms with a technique from parallel string matching, called {\em Deterministic Sampling}.