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The optical spectra of a quantum cascade laser structure under nonequilibrium conditions is studied using the technique of nonequilibrium Green functions. We focus on the impact of Coulomb corrections and their dependence on the operating conditions. The role of the static mean field due to the charge distribution by electrons and ioninzed donors is investigated.
The authors demonstrate operation of a charge readout scheme for quantum dots in a semiconductor nanowire using a quantum point contact defined in a GaAs/AlGaAs two-dimensional electron gas beneath the nanowire. The quantum dots were fabricated by epitaxial growth of InP barriers along a n-type InAs nanowire. Applying negative voltages to two split-gate electrodes aligned to the nanowire induces a
Surface states and traps play an important role in the photophysics of colloidal quantum dots. These states typically lead to large red-shifted photoluminescence. We have used steady-state and time-resolved spectroscopic techniques to investigate the nature of the traps and their lifetimes in colloidal CdSe quantum dots. We conclude that at least two different types of traps contribute to the phot
We investigate universal properties of strongly confined particles that turn out to be dramatically different from what is observed for electrons in atoms and molecules. For a large class of harmonically confined systems, such as small quantum dots and optically trapped atoms, many-body particle addition and removal energies, and energy gaps, are accurately obtained from single-particle eigenvalue
The two main design schemes for Terahertz quantum cascade lasers, based on tunnelling and scattering injection, respectively, are theoretically compared. We apply our simulation package based on the non-equilibrium Green’s function technique. Our results provide a good description of the gain degradation with temperature. Thermal backfilling contributes to decrease of population inversion in both
We study the ground-state properties of a quasi-two-dimensional Bose Einstein condensate of indirect excitons, which are confined in an anisotropic harmonic potential. Incorporating the interactions, we calculate the order parameter variationally. The difficulties in the detection of a Bose-Einstein condensate are also discussed, along with possible ways which would overcome them.
Quantum effects at the nanoscale offer significant potential for future device technologies. A quantum dot heat engine, for instance, is able to convert heat into electrical current. This thesis investigates the transport properties and current fluctuations in a single-level quantum dot heat engine operating in the sequential tunneling regime. Based on the existing experimental data, both the curr
In this paper, a novel detection scheme for the monitoring of insect ecosystems is presented. Our method is based on the remote acquisition of passive sunlight scattering by two insect species. Procedures to identify rare events in remote dark-field spectroscopy are explained. We further demonstrate how to reduce the spectral representation, and how to discriminate between sexes, using a hierarchi
This paper presents a few case studies of finite electron systems for which strong correlations play a dominant role. In simple metal clusters, the valence electrons determine the stability and shape of the clusters. The ionic skeleton of alkali metals is soft, and cluster geometries are often solely determined by electron correlations. In quantum dots and rings, the electrons may be confined by a
We harness the complex mixing process inside a commercial multi-mode fibre to program high-dimensional linear optical circuits for photonic qudits encoded in transverse space and time-of-arrival, and demonstrate their use for high-dimensional entanglement certification.
The injection flow rates of two liquid phases play a decisive role in the slug generation of the liquid-liquid slug flow. However, most injection flow rates so far have been constant. In order to investigate the effects of dynamic injection flow rates on the slug generation, including the slug size, separation distance and slug generation cycle time, a transient numerical model of a cross-junction
Multiple exciton generation (MEG) is a process in which more than one exciton is generated upon the absorption of a high energy photon, typically higher than two times the band gap, in semiconductor nanocrystals. It can be observed experimentally using time resolved spectroscopy such as the transient absorption measurements. Quantification of the MEG yield is usually done by assuming that the bi-e
Popular Abstract in Swedish Målet med arbetet var att öka mängden vindkraft, solel och annan distribuerad generering (DG) som kan anslutas till befintliga distributionsnät på ett snabbt och kostnadseffektivt sätt. Att införa aktiv spänningsreglering i nätet, istället för installation av nya ledningar, har identifierats som en lämplig strategi. Då denna princip bygger på att DG-enheternas produktioDistributed generation (DG), i.e. generation connected to the low and medium voltage distribution network (DN), has been increasing a lot during recent years. Thus the traditional assumption of a unidirectional power flow and a voltage decrease along the distribution feeders is no longer valid in all operation conditions. Voltage control in these networks is often limited to the on-load tap change
dis thesis attempts to use qualitative research and sociological analysis to explore how demilitarization, which TEMPhas lasted for decades, may TEMPhas an impact on development in recent years. Mainly based on literature review and data analysis, dis thesis chose Costa Rica as teh background, for revealing national education status - as teh research object - to speculate on how demilitarization T
