Regensburg 2007 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 44: Semiconductor Microcavities and Entangled States in Quantum Dots

HL 44.4: Invited Talk

Thursday, March 29, 2007, 15:30–16:00, H15

Exciton qubits: From Rabi oscillations towards optoelectronic quantum gates — •Artur Zrenner¹, Stefan Stufler¹, Patrik Ester¹, Steffen Michaelis de Vasconcellos¹, Marc C. Hübner¹, Max Bichler², Pawel Machnikowski³, Vollrath M. Axt⁴, and Tilmann Kuhn⁴ — ¹Universität Paderborn, Warburger Straße 100, D-33098 Paderborn, Germany — ²Walter Schottky Institut, Technische Universität München, Am Coulombwall, D-85748 Garching, Germany — ³Instytut Fizyki Politechniki Wrocławskiej, Wybrzeze Wyspiańskiego 27, PL-50-370 Wrocław, Poland — ⁴Institut für Festkörpertheorie, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Straße 10, D-48149 Münster, Germany

In optical experiments on single self-assembled InGaAs quantum dots we detect the exciton ground state transition as an extremely narrow resonance. For the case of pulsed laser fields and in the absence of decoherence, the ground state exciton represents a qubit. Excitations with ps laser pulses result in multiple qubit rotations, which are demonstrated in a quantitative way as Rabi oscillations in photocurrent experiments. By resonant two-photon excitation we are further able to create and control coherent biexciton states. Under the condition of slight electric field induced detuning we observe Ramsey fringes of a single exciton qubit. In those experiments we are able to demonstrate fringes with a spectral half period below the homogeneous linewidth of the quantum dot. With our results we demonstrate voltage controlled qubit manipulations, which are essential for new types of optoelectronic quantum gates and precision quantum measurements.