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Science 8 August 2003:
Vol. 301. no. 5634, pp. 809 - 811
DOI: 10.1126/science.1083800
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Reports

An All-Optical Quantum Gate in a Semiconductor Quantum Dot

Xiaoqin Li,1 Yanwen Wu,1 Duncan Steel,1* D. Gammon,2 T. H. Stievater,2 D. S. Katzer,2 D. Park,2 C. Piermarocchi,3 L. J. Sham4

We report coherent optical control of a biexciton (two electron-hole pairs), confined in a single quantum dot, that shows coherent oscillations similar to the excited-state Rabi flopping in an isolated atom. The pulse control of the biexciton dynamics, combined with previouslydemonstrated control of the single-exciton Rabi rotation, serves as the physical basis for a two-bit conditional quantum logic gate. The truth table of the gate shows the features of an all-optical quantum gate with interacting yet distinguishable excitons as qubits. Evaluation of the fidelity yields a value of 0.7 for the gate operation. Such experimental capabilityis essential to a scheme for scalable quantum computation bymeans of the optical control of spin qubits in dots.

1 Frontiers in Optical Coherent and Ultrafast Science (FOCUS), Harrison M. Randall Laboratory of Physics, The University of Michigan, Ann Arbor, Michigan 48109–1120, USA.
2 Naval Research Laboratory, Washington, DC 20375–5347, USA.
3 Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824–2320, USA.
4 Department of Physics, The University of California, San Diego, La Jolla, CA 92093–0319, USA.

* To whom correspondence should be addressed. E-mail: dst{at}umich.edu

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