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The article offers information on the study about the impact of coherent tunnelling to a nearby sea of electrons to the optical spectrum of a single quantum dot. The study notes that when an electron combines with the hole, there is a shake-up of the electron sea that establishes rise to characteristic spectral lineshapes. The study infers that the quantum size effects can be tailored to engineer the functionality of semiconductor quantum-dot systems.

Focuses on semiconductor quantum dots. Optical studies of individual quantum dots; Interest in semiconductor quantum dots that interact strongly with light; Details of quantum confinement of electrons; Harnessing quantum mechanical properties.

Tunable exciton relaxation rates are observed in individual vertically coupled semiconductor quantum dots (CQDs). An applied electric field is used to tune the energy difference between the spatially direct (SD) and indirect (SI) excitons in InAs CQDs. The intensity and lifetime of the SI exciton is found to vary as a result of wave-function distribution, carrier tunneling, and phonon-mediated relaxation effects. This includes a modulation of the phonon relaxation rate between the SI and SD excitons, a consequence of momentum space restrictions resulting from the structure factor of the CQD. [ABSTRACT FROM AUTHOR]

Abstract: Using polarization-sensitive photoluminescence and photoluminescence excitation spectroscopy, we study single InAs/GaAs self-assembled quantum dots. The dots were embedded in an n-type, Schottky diode structure allowing for control of the charge state. We present here the exciton, singly charged exciton (positive and negative trions), and the twice negatively charged exciton. For non-resonant excitation below the wetting layer, we observed a large degree of polarization memory from the radiative recombination of both the positive and negative trions. In excitation spectra, through the p-shell, we have found several sharp resonances in the emission from the s-shell recombination of the dot in all charged states. Some of these excitation resonances exhibit strong coulomb shifts upon addition of charges into the quantum dot. One particular resonance of the negatively charged trion was found to exhibit a fine structure doublet under circular polarization. This observation is explained in terms of resonant absorption into the triplet states of the negative trion. [Copyright &y& Elsevier]

Coherent optically driven semiconductor quantum dot systems are proposed for the implementation of quantum information processing devices. Qubits defined in the exciton and spin bases are presented. In particular, single qubit rotation and a two-qubit logic gate have been demonstrated experimentally in the model exciton system. The experimental work done on the exciton system serves as a foundation for future work on spin-based qubits, which possess a much longer coherence lifetime. [Copyright &y& Elsevier]