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15 February 2010 Spin echo of electron spins in semiconductors using ultrafast, small-angle, optical pulses
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Spin-based quantum computing and magnetic resonance techniques rely on the ability to measure the coherence time, T2, of a spin system. We report on the experimental implementation of all-optical spin echo to determine the T2 time of a semiconductor electron-spin system. We use three ultrafast optical pulses to rotate spins an arbitrary angle and measure an echo signal as the time between pulses is lengthened. Unlike previous spin-echo techniques using microwaves, ultrafast optical pulses allow clean T2 measurements of systems with dephasing times (T *2 ) fast in comparison to the timescale for microwave control. We measure a 7 μs coherence time, which is similar to previous measurements in quantum dots and indicates that nuclear spin diffusion is the primary mechanism for decoherence. This demonstration is a critical step towards optical, dynamic decoupling, which can eliminate fast decoherence and can be integrated into quantum computer architectures based on opticallycontrolled spin qubits.
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Susan M. Clark, Kai-Mei C. Fu, Qiang Zhang, Thaddeus D. Ladd, Colin R. Stanley, and Yoshihisa Yamamoto "Spin echo of electron spins in semiconductors using ultrafast, small-angle, optical pulses", Proc. SPIE 7611, Advances in Photonics of Quantum Computing, Memory, and Communication III, 76110J (15 February 2010);

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