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Experimental realization of a quantum algorithm


Quantum computers1,2,3,4,5 can in principle exploit quantum-mechanical effects to perform computations (such as factoring large numbers or searching an unsorted database) more rapidly than classical computers1,2,6,7,8. But noise, loss of coherence, and manufacturing problems make constructing large-scale quantum computers difficult9,10,11,12,13. Although ion traps and optical cavities offer promising experimental approaches14,15, no quantum algorithm has yet been implemented with these systems. Here we report the experimental realization of a quantum algorithm using a bulk nuclear magnetic resonance technique16,17,18, in which the nuclear spins act as ‘quantum bits’19. The nuclear spins are particularly suited to this role because of their natural isolation from the environment. Our simple quantum computer solves a purely mathematical problem in fewer steps than is possible classically, requiring fewer ‘function calls’ than a classical computer to determine the global properties of an unknown function.

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Figure 1: Quantum circuit for performing the D-J algorithm.
Figure 2: Proton spectrum after completion of theD-J algorithm and a single read-out pulse XA,with an effectively pure.
Figure 3: Experimentally measured and theoretically expected deviation density matrices after completion of the D-J algorithm.

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We thank A. Pines and M. Kubinec for discussion. This work was supported by DARPA under the NMRQC and QUIC initiatives. L.V. gratefully acknowledges a Francqui Fellowship of the Belgian American Educational Foundation and a Yansouni Family Fellowship.

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Correspondence to Isaac L. Chuang.

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Chuang, I., Vandersypen, L., Zhou, X. et al. Experimental realization of a quantum algorithm. Nature 393, 143–146 (1998).

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