Engineering the spatial confinement of exciton-polaritons in semiconductors

We demonstrate the spatial confinement of electronic excitations in a solid state system, within novel artificial structures that can be designed having arbitrary dimensionality and shape. The excitations under study are exciton-polaritons in a planar semiconductor microcavity. They are confined within a micron-sized region through lateral trapping of their photon component. Striking signatures of confined states of lower and upper polaritons are found in angle-resolved light emission spectra, where a discrete energy spectrum and broad angular patterns are present. A theoretical model supports unambiguously our observations

Backflashes from fast-gated avalanche photodiodes in quantum key distribution

InGaAs single-photon avalanche photodiodes (APDs) are key enablers for high-bit rate quantum key distribution. However, the deviation of such detectors from ideal models can open side-channels for an eavesdropper, Eve, to exploit. The phenomenon of backflashes, whereby APDs reemit photons after detecting a photon, gives Eve the opportunity to passively learn the information carried by the detected photon without the need to actively interact with the legitimate receiver, Bob. While this has been observed in slow-gated detectors, it has not been investigated in fast-gated APDs where it has been posited that this effect would be lessened. Here, we perform the first experiment to characterize the security threat that backflashes provide in a GHz-gated self-differencing APD using the metric of information leakage. We find that, indeed, the information leakage is lower than that reported for slower-gated detectors, and we show that its effect on the secure key rate is negligible. We also relate the rate of backflash events to the APD dark current, thereby suggesting that their origin is the InP multiplication region in the APD

Independent indistinguishable quantum light sources on a reconfigurable photonic integrated circuit

We report a compact, scalable, quantum photonic integrated circuit realised by combining multiple, independent InGaAs/GaAs quantum-light-emitting-diodes (QLEDs) with a silicon oxynitride waveguide circuit. Each waveguide joining the circuit can then be excited by a separate, independently electrically contacted QLED. We show that the emission from neighbouring QLEDs can be independently tuned to degeneracy using the Stark Effect and that the resulting photon streams are indistinguishable. This enables on-chip Hong-Ou-Mandel-type interference, as required for many photonic quantum information processing schemes.Comment: 15 pages, 5 figure

Dimethyl fumarate attenuates reactive microglia and long-term memory deficits following systemic immune challenge

BACKGROUND: Systemic inflammation is associated with increased cognitive decline and risk for Alzheimer's disease. Microglia (MG) activated during systemic inflammation can cause exaggerated neuroinflammatory responses and trigger progressive neurodegeneration. Dimethyl fumarate (DMF) is a FDA-approved therapy for multiple sclerosis. The immunomodulatory and anti-oxidant properties of DMF prompted us to investigate whether DMF has translational potential for the treatment of cognitive impairment associated with systemic inflammation. METHODS: Primary murine MG cultures were stimulated with lipopolysaccharide (LPS) in the absence or presence of DMF. MG cultured from nuclear factor (erythroid-derived 2)-like 2-deficient (Nrf2 -/- ) mice were used to examine mechanisms of DMF actions. Conditioned media generated from LPS-primed MG were used to treat hippocampal neuron cultures. Adult C57BL/6 and Nrf2 -/- mice were subjected to peripheral LPS challenge. Acute neuroinflammation, long-term memory function, and reactive astrogliosis were examined to assess therapeutic effects of DMF. RESULTS: DMF suppressed inflammatory activation of MG induced by LPS. DMF suppressed NF-κB activity through Nrf2-depedent and Nrf2-independent mechanisms in MG. DMF treatment reduced MG-mediated toxicity towards neurons. DMF suppressed brain-derived inflammatory cytokines in mice following peripheral LPS challenge. The suppressive effect of DMF on neuroinflammation was blunted in Nrf2 -/- mice. Importantly, DMF treatment alleviated long-term memory deficits and sustained reactive astrogliosis induced by peripheral LPS challenge. DMF might mitigate neurotoxic astrocytes associated with neuroinflammation. CONCLUSIONS: DMF treatment might protect neurons against toxic microenvironments produced by reactive MG and astrocytes associated with systemic inflammation

Optical manipulation of the wave function of quasiparticles in a solid

Polaritons in semiconductor microcavities are hybrid quasiparticles consisting of a superposition of photons and excitons. Due to the photon component, polaritons are characterized by a quantum coherence length in the several micron range. Owing to their exciton content, they display sizeable interactions, both mutual and with other electronic degrees of freedom. These unique features have produced striking matter wave phenomena, such as Bose-Einstein condensation, or parametric processes able to generate quantum entangled polariton states. Recently, several paradigms for spatial confinement of polaritons in semiconductor devices have been established. This opens the way to quantum devices in which polaritons can be used as a vector of quantum information. An essential element of each quantum device is the quantum state control. Here we demonstrate control of the wave function of confined polaritons, by means of tailored resonant optical excitation. By tuning the energy and momentum of the laser, we achieve precise control of the momentum pattern of the polariton wave function. A theoretical model supports unambiguously our observations

Spatial dynamics of confined semiconductor microcavity polaritons

We report on the dynamics of confined zero-dimensional polaritons. We excite resonantly discrete polariton states optically with a tailored picosecond laser pulse and observe their emission time resolved in the two-dimensional k space or real space. We are able to distinguish between three regimes. When the laser excites only one state no dynamics are observed. When a small number of well separated states are excited, the dynamics are described in terms of interference. When a quasicontinuum of states is excited, the dynamics are described in terms of ballistically propagating two-dimensional (2D) polaritons which scatter elastically at the potential barriers. The measured propagation velocities are reproduced with the theory of 2D polaritons, which sustains our interpretation

Sox17 and ß-catenin co-occupy Wnt-responsive enhancers to govern the endoderm gene regulatory network

© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Mukherjee, S., Chaturvedi, P., Rankin, S. A., Fish, M. B., Wlizla, M., Paraiso, K. D., MacDonald, M., Chen, X., Weirauch, M. T., Blitz, I. L., Cho, K. W. Y., & Zorn, A. M. Sox17 and ß-catenin co-occupy Wnt-responsive enhancers to govern the endoderm gene regulatory network. Elife, 9, (2020): e58029, doi:10.7554/eLife.58029.Lineage specification is governed by gene regulatory networks (GRNs) that integrate the activity of signaling effectors and transcription factors (TFs) on enhancers. Sox17 is a key transcriptional regulator of definitive endoderm development, and yet, its genomic targets remain largely uncharacterized. Here, using genomic approaches and epistasis experiments, we define the Sox17-governed endoderm GRN in Xenopus gastrulae. We show that Sox17 functionally interacts with the canonical Wnt pathway to specify and pattern the endoderm while repressing alternative mesectoderm fates. Sox17 and β-catenin co-occupy hundreds of key enhancers. In some cases, Sox17 and β-catenin synergistically activate transcription apparently independent of Tcfs, whereas on other enhancers, Sox17 represses β-catenin/Tcf-mediated transcription to spatially restrict gene expression domains. Our findings establish Sox17 as a tissue-specific modifier of Wnt responses and point to a novel paradigm where genomic specificity of Wnt/β-catenin transcription is determined through functional interactions between lineage-specific Sox TFs and β-catenin/Tcf transcriptional complexes. Given the ubiquitous nature of Sox TFs and Wnt signaling, this mechanism has important implications across a diverse range of developmental and disease contexts.Eunice Kennedy Shriver National Institute of Child Health and Human Development (HD073179) Ken WY Cho Aaron M Zorn National Institute of Diabetes and Digestive and Kidney Diseases (P30DK078392) Aaron M Zorn Eunice Kennedy Shriver National Institute of Child Health and Human Development (P01HD093363) Aaron M Zor

Collisional damping of dipole oscillations in a trapped polariton gas

We study the relaxation dynamics of a trapped polariton gas in the nonlinear regime. We excite the three lowest energy states of the system and observe the time evolution of the polariton density in the momentum space. At a low excitation power, the dynamics is characterized by dipole oscillations of constant amplitude. A damping of these oscillations is observed at a high excitation power. It is attributed to collisional relaxation within the coherent polariton gas. We investigate the dependence of this effect on the excitation power, polarization, and polariton excitonic content to highlight the role of polariton-polariton scattering. The experiments are described in the frame of a Gross-Pitaevskii mean-field theory. We find a good agreement between the theoretical simulations and the experimental observations. Analysis of the theoretical model reveals that multiple parametric scattering and final-state stimulation are responsible for the damping of the oscillations

Evaluation of the Performance of Expanded Immunization Programme Supply Chain and Logistics Management in Southern Benin Rural Health District

Abstract The objective was to evaluate the performance of the expanded immunization programme's (EPI) supply chain of and logistics management in Comé health district in 2015. This cross-sectional and evaluative study concerned the central deposit of vaccines and 19 health care centers randomly selected. Data on the performance of EIP supply chain of and logistics management were collected from 5 to 30 March 2015 using direct observation, document exploitation, questionnaire and individual interview in 20 health workers directly involved in EIP activities and 59 mothers of children aged 0-11 months. The performance of the supply chain and logistics management was assessed through three components "structure", "process" and "results" using predetermined score of two scales seeking for achievement of criterions included in components. The overall performance of the EIP's supply chain and logistics in the health district of Comé was rated fair (score = 75.2%). The performance level was good for "structure" (score = 90.3%), acceptable for the "process" (score = 79, 85%) and poor for the "results" of the management of supply chain and logistics (score = 59.48%). The level of performance EIP supply chain and logistics was sub-optimal. Adequate measures should be considered to improve the component "result" of the EIP supply chain and logistics management in the health district of Comé

Gigahertz measurement-device-independent quantum key distribution using directly modulated lasers

Measurement-device-independent quantum key distribution (MDI-QKD) is a technique for quantum-secured communication that eliminates all detector side-channels, although is currently limited by implementation complexity and low secure key rates. Here, we introduce a simple and compact MDI-QKD system design at gigahertz clock rates with enhanced resilience to laser fluctuations—thus enabling free-running semiconductor laser sources to be employed without spectral or phase feedback. This is achieved using direct laser modulation, carefully exploiting gain-switching and injection-locking laser dynamics to encode phase-modulated time-bin bits. Our design enables secure key rates that improve upon the state of the art by an order of magnitude, up to 8 bps at 54 dB channel loss and 2 kbps in the finite-size regime for 30 dB channel loss. This greatly simplified MDI-QKD system design and proof-of-principle demonstration shows that MDI-QKD is a practical, high-performance solution for future quantum communication networks