An All-Optical Quantum Gate in a Semiconductor Quantum Dot

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Science  08 Aug 2003:
Vol. 301, Issue 5634, pp. 809-811
DOI: 10.1126/science.1083800

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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.

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