Recent advances in exciton based quantum information processing in quantum dot nanostructures

Recent experimental developments in the field of semiconductor quantum dot spectroscopy will be discussed. First we report about single quantum dot exciton two-level systems and their coherent properties in terms of single qubit manipulations. In the second part we report on coherent quantum coupling in a prototype "two-qubit" system consisting of a vertically stacked pair of quantum dots. The interaction can be tuned in such quantum dot molecule devices using an applied voltage as external parameter.Comment: 37 pages, 15 figures, submitted to New Journal of Physics, focus issue on Solid State Quantum Information, added reference

Central academic facility of the University of Paderborn

Artur Zrenner ; Center for Optoelectronics and Photonics Paderbor

Polarization-entangled twin photons from two-photon quantum-dot emission

Semiconductor quantum dots are promising sources for polarization-entangled photons. As an alternative to the usual cascaded biexciton-exciton emission, direct two-photon emission from the biexciton can be used. With a high-quality optical resonator tuned to half the biexciton energy, a large proportion of the photons can be steered into the two-photon emission channel. In this case the degree of polarization entanglement is inherently insensitive to the exciton fine-structure splitting. In the present work we analyze the biexciton emission with particular emphasis on the influence of coupling of the quantum-dot cavity system to its environment. Especially for a high-quality cavity, the coupling to the surrounding semiconductormaterial can open up additional phonon-assisted decay channels. Our analysis demonstrates that with the cavity tuned to half the biexciton energy, the potentially detrimental influence of the phonons on the polarization entanglement is strongly suppressed-high degrees of entanglement can still be achieved. We further discuss spectral properties and statistics of the emitted twin photons.DFG [TRR142, GRK1464]; BMBF through Q.com [16KIS0114]; Heisenberg programme of the DFGThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Spatially Resolved Spectroscopy of Single and Coupled Quantum Dots

Optical properties of single and coupled quantum dots are studied with high spatial resolution. Several techniques are used to resolve spectra of individual dots. Spatially isolated dots produced by double cleaved edge overgrowth are investigated by diffraction limited spectroscopy using a special microscope setup. Self-assembled InGaAs dots have been investigated by near-field optical techniques with metallic masks and by scanning tunneling microscopy cathodoluminescence. Photoluminescence and photoluminescence excitation spectra of selected quantum dots are discussed which reveal detailed information on ground and excited states as well as their coupling with neighboring dots

Direct Observation of Hole Edge Channels in a Two Dimensional Electron Gas

We report the direct optical observation of confinement and transport of minority holes in a two dimensional electron gas. In spatially resolved magneto-optical experiments we observe hole confinement at the edge of a two dimensional electron gas and hole transport in edge channels. In a theoretical analysis we show that a repulsive edge potential for holes at the boundary of a two dimensional electron gas is caused by a polaron effect