Ultrafast optical rotations of electron spins in quantum dots

Coherent manipulation of quantum bits (qubits) on timescales much shorter than the coherence time1,2 is a key prerequisite for quantum information processing. Electron spins in quantum dots

are particularly attractive for implementations of qubits, and efficient optical methods for initialization and readout of spins have been developed in recent years3,4. Spin coherence times

in the microsecond range have been demonstrated5. Therefore, spin control by picosecond optical pulses would be highly desirable so that a large number of spin rotations could be carried out

while coherence is maintained. A major remaining challenge is demonstration of such rotations with high fidelity. Here, we use an ensemble of quantum-dot electron spins focused into a small

number of precession modes about a magnetic field by periodic optical pumping. We demonstrate ultrafast optical rotations of spins about arbitrary axes on a picosecond timescale using laser

pulses as control fields.

This work was supported by the Bundesministerium für Bildung and Forschung program ‘nanoquit’, the Office of Naval Research and the Deutsche Forschungsgemeinschaft. S.E.E. was an NRC/NRL

Research Associate during this work.

Experimentelle Physik 2, Technische Universität Dortmund, 44221 Dortmund, Germany

A. F. Ioffe Physico-Technical Institute, Russian Academy of Sciences, 194021, St. Petersburg, Russia

Angewandte Festkörperphysik, Ruhr-Universität Bochum, 44780 Bochum, Germany

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