Fast preparation of single hole spin in InAs/GaAs quantum dot in Voigt geometry magnetic field

The preparation of a coherent heavy-hole spin via ionization of a spin-polarized electron-hole pair in an InAs/GaAs quantum dot in a Voigt geometry magnetic field is investigated. For a dot with a 17 ueV bright-exciton fine-structure splitting, the fidelity of the spin preparation is limited to 0.75, with optimum preparation occurring when the effective fine-structure of the bright-exciton matches the in-plane hole Zeeman energy. In principle, higher fidelities can be achieved by minimizing the bright-exciton fine-structure splitting.Comment: 8 pages, 10 figs, published PRB 85 155310 (2012

Polarization bistability and resultant spin rings in semiconductor microcavities

The transmission of a pump laser resonant with the lower polariton branch of a semiconductor microcavity is shown to be highly dependent on the degree of circular polarization of the pump. Spin dependent anisotropy of polariton-polariton interactions allows the internal polarization to be controlled by varying the pump power. The formation of spatial patterns, spin rings with high degree of circular polarization, arising as a result of polarization bistability, is observed. A phenomenological model based on spin dependent Gross-Pitaevskii equations provides a good description of the experimental results. Inclusion of interactions with the incoherent exciton reservoir, which provides spin-independent blueshifts of the polariton modes, is found to be essential.Comment: 5 pages, 3 figure

Voltage Controlled Hot Carrier Injection Enables Ohmic Contacts Using Au Island Metal Films on Ge

We introduce a new approach to creating low-resistance metalsemiconductor ohmic contacts, illustrated using high conductivity Au island metal films (IMFs) on Ge, with hot carrier injection initiated at low applied voltage. The same metallization process simultaneously allows ohmic contact to n-Ge and p-Ge, because hot carriers circumvent the Schottky barrier formed at metal/n-Ge interfaces. A 2.5x improvement in contact resistivity is reported over previous techniques to achieve ohmic contact to both n- and p- semiconductor. Ohmic contacts at 4.2 K confirm nonequilibrium current transport. Self-assembled Au IMFs are strongly orientated to Ge by annealing near the Au/Ge eutectic temperature. Au IMF nanostructures form, provided the Au layer is below a critical thickness. We anticipate that optimized IMF contacts may have applicability to many material systems. Optimizing this new paradigm for metalsemiconductor contacts offers the prospect of improved nanoelectronic systems and the study of voltage controlled hot holes and electrons.Peer reviewe

Ultrafast Depopulation of a Quantum Dot by LA-phonon-assisted Stimulated Emission

We demonstrate ultrafast \emph{incoherent} depopulation of a quantum dot from above to below the transparency point using LA-phonon-assisted emission stimulated by a red-shifted laser pulse. The QD is turned from a weakly vibronic system into a strongly vibronic one by laser driving which enables the phonon-assisted relaxation between the excitonic components of two dressed states. The depopulation is achieved within a laser pulse-width-limited time of 20~ps and exhibits a broad tuning range of a few meV. Our experimental results are well reproduced by path-integral calculations

Dynamic vibronic coupling in InGaAs quantum dots

The electron-phonon coupling in self-assembled InGaAs quantum dots is relatively weak at low light intensities, which means that the zero-phonon line in emission is strong compared to the phonon sideband. However, the coupling to acoustic phonons can be dynamically enhanced in the presence of an intense optical pulse tuned within the phonon sideband. Recent experiments have shown that this dynamic vibronic coupling can enable population inversion to be achieved when pumping with a blue-shifted laser and for rapid de-excitation of an inverted state with red detuning. In this paper we confirm the incoherent nature of the phonon-assisted pumping process and explore the temperature dependence of the mechanism. We also show that a combination of blue- and red-shifted pulses can create and destroy an exciton within a timescale ∼ 20 ps determined by the pulse duration and ultimately limited by the phonon thermalisation time

Phonon-Assisted Population Inversion of a Single InGaAs/GaAs Quantum Dot by Pulsed Laser Excitation

We demonstrate a new method to realize the population inversion of a single InGaAs/GaAs quantum dot excited by a laser pulse tuned within the neutral exciton phonon sideband. In contrast to the conventional method of inverting a two-level system by performing coherent Rabi oscillation, the inversion is achieved by rapid thermalization of the optically dressed states via incoherent phonon-assisted relaxation. A maximum exciton population of 0.67±0.06 is measured for a laser tuned 0.83 meV to higher energy. Furthermore, the phonon sideband is mapped using a two-color pump-probe technique, with its spectral form and magnitude in very good agreement with the result of path-integral calculations

Mind the gap? Civil society policy engagement and the pursuit of gender justice: critical discourse analysis of the implementation of the Beijing Declaration and Platform for Action in Africa 2003–2015

This article presents critical discourse analysis of state and civil society organisations’ efforts to implement the gender mainstreaming goals set out in the United Nations’ Beijing Declaration. It is argued that the latter represents a generational opportunity to apply a Feminist Political Economic Framework to development in Africa. However, the research findings show how current practice falls short of the sought-after participative democratic model of mainstreaming. Instead, analysis reveals significant differences in state and civil society organisations’ policy framing, issues over conceptual clarity and a disjuncture in state and civil society prioritisation of key gendered issues such as poverty, economic inequality and conflict resolution. This matters because it indicates that the capacity of the civil sphere to act as a political arena from which NGOs may challenge the traditionally male-dominated power structures is being undermined by a ‘disconnect’ between state and civil society as they pursue contrasting agendas

Cytokines and Inflammatory Mediators [30-39]: 30. The LPS Stimulated Production of Interleukin-10 is not Associated with -819C/T and -592C/A Promoter Polymorphisms in Healthy Indian Subjects

Background: Interleukin-10 is a pivotal immunoregulatory cytokine with pleiotropic effects on the immune system. IL-10 promoter polymorphisms have been associated with disease susceptibility and the ability to secrete IL-10 in vitro. We suspected that the association of the widely studied -819C/T and -592C/A polymorphisms with the IL-10 production might vary between ethnic groups. Therefore, we examined the association of -819 C/T and -592 C/A promoter polymorphisms with in vitro LPS stimulated secretion of IL-10 in normal healthy Indian volunteers. Methods: Peripheral blood was collected from 103 healthy volunteers and diluted whole blood cultures were set up with 100 ng/ml of LPS as stimulant: supernatant was collected at 24 h and IL-10 levels were assayed by ELISA. Genotyping was done for -819C/T polymorphism in 101 individuals and -592C/A polymorphism in 68 individuals by polymerase chain reaction followed by RFLP. The differences in IL-10 production between the genotypes were analysed by ANOVA. Results: There were 30, 47 and 24 individuals with the CC, CT and TT genotypes with a minor allele (T) frequency of 47% for the -819C/T polymorphism. The CC and TT genotypes at position -819 were strongly associated with CC and AA genotypes at -592 position suggestive of strong linkage disequilibrium. There was no association between the -819 genotype and the in vitro LPS stimulated IL-10 levels. Conclusions: The -819C/T and the -592 C/A polymorphisms of the IL-10 promoter region are not significantly associated with LPS stimulated IL-10 production healthy Indian subjects. Disclosure statement: All authors have declared no conflicts of interes