Article abstract
Nature Physics 5, 352 - 356 (2009)
Published online: 29 March 2009 | doi:10.1038/nphys1229
Subject Categories: Nanotechnology | Electronics, photonics and device physics
Femtosecond few-fermion dynamics and deterministic single-photon gain in a quantum dot
Florian Sotier1, Tim Thomay1, Tobias Hanke1, Jan Korger1, Suddhasatta Mahapatra2, Alexander Frey2, Karl Brunner2, Rudolf Bratschitsch1 & Alfred Leitenstorfer1
Abstract
The ability to coherently manipulate single electron and photon states is vital for quantum information processing. However, typical quantization and correlation energies restrict processing rates in real implementations owing to the time–energy uncertainty. Here we report optical initialization, manipulation and probing of a single CdSe/ZnSe semiconductor quantum dot on femtosecond timescales, the ultimate limit for clean quantum operations in such 'artificial atoms'. Resonant pump–probe measurements on a donor-charged quantum dot reveal that the fundamental exciton absorption is switched off through instantaneous Coulomb renormalization. Optical gain builds up following ultrafast intraband relaxation, with a thermalization rate determined by the electron spin. Operating the system in a nonlinear regime, we demonstrate the ability to change the number of quanta in a femtosecond light pulse by exactly 
1. This deterministic single-photon amplifier is characterized by a flat gain spectrum.
- Department of Physics and Center for Applied Photonics, University of Konstanz, D-78457 Konstanz, Germany
- Institute of Physics, EP 3, University of Würzburg, D-97074 Würzburg, Germany
Correspondence to: Alfred Leitenstorfer1 e-mail: aleitens@uni-konstanz.de
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