Monday, August 5, 2013

1308.0588 (Zhan Shi et al.)

Fast coherent manipulation of three-electron states in a double quantum

Zhan Shi, C. B. Simmons, Daniel R. Ward, J. R. Prance, Xian Wu, Teck Seng Koh, John King Gamble, D. E. Savage, M. G. Lagally, Mark Friesen, S. N. Coppersmith, M. A. Eriksson
A fundamental goal in the manipulation of quantum systems is the achievement of many coherent oscillations within the characteristic dephasing time T2*[1]. Most manipulations of electron spins in quantum dots have focused on the construction and control of two-state quantum systems, or qubits, in which each quantum dot is occupied by a single electron[2-7]. Here we perform quantum manipulations on a system with more electrons per quantum dot, in a double dot with three electrons. We demonstrate that tailored pulse sequences can be used to induce coherent rotations between 3-electron quantum states. Certain pulse sequences yield coherent oscillations with a very high figure of merit (the ratio of coherence time to rotation time) of >100. The presence of the third electron enables very fast rotations to all possible states, in contrast to the case when only two electrons are used, in which some rotations are slow. The minimum oscillation frequency we observe is >5 GHz.
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