Incoherent excitation and switching of spin states in exciton-polariton condensates

We investigate, theoretically and numerically, the spin dynamics of a two-component exciton-polariton condensate created and sustained by non-resonant spin-polarized optical pumping of a semiconductor microcavity. Using the open-dissipative mean-field model, we show that the existence of well defined phase-locked steady states of the condensate may lead to efficient switching and control of spin (polarization) states with a non-resonant excitation. Spatially inhomogeneous pulsed excitations can cause symmetry breaking in the pseudo-spin structure of the condensate and lead to formation of non-trivial spin textures. Our model is universally applicable to two weakly coupled polariton condensates, and therefore can also describe the behaviour of condensate populations and phases in 'double-well' type potentials

Device independent state estimation based on Bell's inequalities

The only information available about an alleged source of entangled quantum states is the amount $S$ by which the Clauser-Horne-Shimony-Holt (CHSH) inequality is violated: nothing is known about the nature of the system or the measurements that are performed. We discuss how the quality of the source can be assessed in this black-box scenario, as compared to an ideal source that would produce maximally entangled states (more precisely, any state for which $S=2\sqrt{2}$). To this end, we introduce several inequivalent notions of fidelity, each one related to the use one can make of the source after having assessed it; and we derive quantitative bounds for each of them in terms of the violation $S$. We also derive a lower bound on the entanglement of the source as a function of $S$ only.Comment: 8 pages, 2 figures. Added appendices containing proof

Characteristics of an exploited tropical shallow - water demersal fish community in Malaysia

Trawling provided insights into the characteristics of an exploited tropical shallow-water demersal fish community. A total of 6,565 fish specimens weighing 285 kg were caught at 20 sampling stations. In all,139 species belonging to 50 families were recorded. The major families ranked by weight were Dasyatidae (19.7%), Synodontidae (18.3%), Paralichthyidae (8.9%), Dactylopteridae (8%), Nemipteridae (5.3%), Lagocephalidae (5.2%), Priacanthidae (5%); and Mullidae (4%). The overall fish trawled consisted of 53% food fish and 47% trash fish. The demersal fish community could be partitioned into four trophic groups, i.e., large zoobenthos feeders, intermediate predators, small demersal zoobenthos feeders and small demersal zooplankton feeders. Small crustaceans played an important role as food resources for all the trophic groups. They were the major food for small demersal zoobenthos feeders, the dominant group, and large zoobenthos feeders. Analysis of growth characteristics of ten common species using length-frequency data showed that Saurlda elongata and Trachlnocephalus myops ·(Synodontidae) and Dactyloptena orlentalis (Daetylopteridae) had higher growth rates than the other fishes in the community. Exploitation rates of these three species by trawlers were also high although they have little commercial value. Annual recruitment patterns. for the demersal fishes were generally protracted showing a single pulse, although some species have a second minor pulse

Bistability in Microcavities with Incoherent Optical or Electrical Excitation

We consider a quantum well embedded in a zero-dimensional microcavity with a sub-wavelength grated mirror, where the x-linearly polarized exciton mode is strongly coupled to the cavity photon, while y-polarized excitons remain in the weak coupling regime. Under incoherent optical or electric pumping, we demonstrate polariton bistability associated with parametric scattering processes. Such bistability is useful for constructing polaritonic devices with optical or electrical incoherent pumping.Comment: 5 pages, 3 figure

Instability-induced formation and non-equilibrium dynamics of phase defects in polariton condensates

We study, theoretically and numerically, the onset and development of modulational instability in an incoherently pumped spatially homogeneous polariton condensate. Within the framework of mean-field theory, we identify regimes of modulational instability in two cases: 1) Strong feedback between the condensate and reservoir, which may occur in scalar condensates, and 2) Parametric scattering in the presence of polarization splitting in spinor condensates. In both cases we investigate the instability induced textures in space and time including non-equilibrium dynamics of phase dislocations and vortices. In particular we discuss the mechanism of vortex destabilization and formation of spiraling waves. We also identify the presence of topological defects, which take the form of half-vortex pairs in the spinor case, giving an "eyelet" structure in intensity and dipole type structure in the spin polarization. In the modulationally stable parameter domains, we observe formation of the phase defects in the process of condensate formation from an initially spatially incoherent low-density state. In analogy to the Kibble-Zurek type scaling for nonequilibrium phase transitions, we find that the defect density scales with the pumping rate.Comment: 13 pages, 9 figures, revised manuscript sent to Phys. Rev.

HIV and Housing Insecurity in Louisiana

This study sought to assign the parishes in Louisiana into distinctive spatial-temporal clusters based on their trends in HIV prevalence and percentages of households with severe housing problems and to assess the parish’s resilience and susceptibility to HIV infection given its pre- existing sociodemographic conditions. Results revealed that trends in the HIV prevalence rates and percentages of households with severe housing problems differed across the five distinct spatial-temporal clusters. The percentage of households with severe housing problems and the percentage of non-Hispanic Black population were positively associated with the HIV prevalence rate while the reverse was true for the percentage of population below 18 years of age and physician density. Efforts to minimize the detrimental effects of HIV infection and/or housing insecurity should focus on Allen, East Baton Rouge, East Feliciana, Orleans, Iberville, and West Feliciana parishes

Learning knowledge management concepts via the use of a scenario building tool on an e-learning platform

Author name used in this publication: Teresa B. Y. LiewAuthor name used in this publication: Patrick S. W. FongAuthor name used in this publication: Adela LauRefereed conference paper2009-2010 > Academic research: refereed > Refereed conference paperAccepted ManuscriptPublishe

Spin rings in bi-stable planar semiconductor microcavities

A unique feature of exciton-polaritons, inherited from their mixed light-matter origin, is the strongly spin-dependent polariton-polariton interaction, which has been predicted to result in the formation of spin rings in real space [Shelykh et al., Phys. Rev. Lett. 100, 116401 (2008)]. Here we experimentally demonstrate the spin bi-stability of exciton-polaritons in an InGaAs-based semiconductor microcavity under resonant optical pumping. We observe the formation of spin rings whose size can be finely controlled in a spatial scale down to the micrometer range, much smaller than the spot size. We additionally evaluate the sign and magnitude of the antiparallel polariton spin interaction constant.Comment: 5 pages, 4 figure

Characterisation of Bidor Kaolinite and Illite

Two types of commercial clay minerals from the Bidor region of Perak were studied. From the X-ray diffraction study, these clays were identified as disordered kaolinite and 2 M polymorph of illite. The morphologies, the surface properties, the pore structures and the infrared absorption properties were examined. The basis for the identification of these clays is discussed

Electrically pumped semiconductor laser with low spatial coherence and directional emission

We design and fabricate an on-chip laser source that produces a directional beam with low spatial coherence. The lasing modes are based on the axial orbit in a stable cavity and have good directionality. To reduce the spatial coherence of emission, the number of transverse lasing modes is maximized by fine-tuning the cavity geometry. Decoherence is reached in a few nanoseconds. Such rapid decoherence will facilitate applications in ultrafast speckle-free full-field imaging