Quantum algorithm: Difference between revisions

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===Evaluating NAND trees===
 
The problem is to compute the value of a formula given by a balanced binary tree with bits at the leaves, and NAND gates at the inner vertices.<ref>{{cite web |url=http://scottaaronson.com/blog/?p=207 |title=NAND now for something completely different |author=[[Scott Aaronson]] |date=2007-02-03 |work=Shtetl-Optimized |accessdate=2009-12-17}}</ref> This problem requires Θ(''N''<sup>0.753c</sup>) queries classicallyusing randomness (where <math>c = \log_2(1+\sqrt{33})-2 \approx 0.754</math>), but can be solved in Θ(''N''<sup>0.5</sup>) queries by a quantum algorithm.<ref>E. Farhi, [[Jeffrey Goldstone|J. Goldstone]], and S. Gutmann, A quantum algorithm for the Hamiltonian NAND tree, Theory of Computing 4 (2008), no. 1, 169–190, quant-ph/0702144</ref>
 
==BQP-complete problems==