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Implementation of a quantum search algorithm on a quantum computer


In 1982 Feynman1 observed that quantum-mechanical systems have an information-processing capability much greater than that of corresponding classical systems, and could thus potentially be used to implement a new type of powerful computer. Three years later Deutsch2 described a quantum-mechanical Turing machine, showing that quantum computers could indeed be constructed. Since then there has been extensive research in this field, but although the theory is fairly well understood, actually building a quantum computer has proved extremely difficult. Only two methods have been used to demonstrate quantum logic gates: ion traps3,4 and nuclear magnetic resonance (NMR)5,6. NMR quantum computers have recently been used to solve a simple quantum algorithm—the two-bit Deutsch problem7,8. Here we show experimentally that such a computer can be used to implement a non-trivial fast quantum search algorithm initially developed by Grover9,10, which can be conducted faster than a comparable search on a classical computer.

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Figure 1: A quantum circuit for the implementation of a quantum search algorithm on a two-qubit computer.
Figure 2: NMR pulse sequence used to implement U f a b .
Figure 3: Experimental spectra from our NMR quantum computer.


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We thank A. Ekert for discussions; J.A.J. thanks C. M. Dobson for encouragement. This is a contribution from the Oxford Centre for Molecular Sciences, which is supported by the UK EPSRC, BBSRC and MRC. M.M. thanks CESG (UK) for their support. R.H.H. thanks the Danish Research Academy for financial assistance.

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Correspondence to Jonathan A. Jones.

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Jones, J., Mosca, M. & Hansen, R. Implementation of a quantum search algorithm on a quantum computer. Nature 393, 344–346 (1998).

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