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Polarized |S|=0.99±0.01$| S | = 0.99 \pm 0.01$, and unpolarized |S|=0.03±0.01$| S | = 0.03 \pm 0.01$ emission from a single emitter embedded in a single, cylindrically symmetric device design is presented. The polarization stems from a position offset of the single emitter with respect to the cavity center, which breaks the cylindrical symmetry, and a position‐dependent coupling to the frequency degenerate eigenmodes of the resonator structure is shown. The experimental results are interpreted by using numerical simulations and by experimental mapping of the polarization‐resolved far‐field emission patterns. The findings can be generalized to any nanophotonic structure where two orthogonal eigenmodes are not fully spatially overlapping. [ABSTRACT FROM AUTHOR]

The collection of single‐photon emission from a quantum dot (QD) in a Bragg waveguide through a photonic wire bond (PWB) via free‐space resonant frequency pumping at 1.6 K is demonstrated. The in‐fiber single photons show a small multiphoton contribution, quantified by a low second order photon autocorrelation value of gcorr(2)(0)=(5.9±0.8)×10−3$g_{{\mathrm{corr}}}^{(2)}\;(0) = ({5.9 \pm 0.8})\; \times {10^{ - 3}}$ (background‐corrected) or graw(2)(0)=(9.5±1.4)×10−2$g_{{\mathrm{raw}}}^{(2)}(0)\; = ({9.5 \pm 1.4})\; \times {10^{ - 2}}{\mathrm{\;}}$(raw data). The decay time of the QD is measured to be τ=440${\mathrm{\tau \;}} = {\mathrm{\;}}440$ ps. The PWB obviates the need for in‐cryostat alignment of the single‐photon source with an optical fiber and thus offers a route to scalable integration of quantum photonic devices in a cryogenic environment. Uniquely, the approach combines the QD‐waveguide technique, enabling resonant driving of individual QDs without the need for cross‐polarization filtering, and the PWB for deterministic, alignment‐free coupling of single‐photon sources to optical fibers. [ABSTRACT FROM AUTHOR]

Purcell‐enhanced quantum dot single‐photon emission in the telecom C‐band from InAs quantum dots inside circular Bragg grating cavities is shown. The InAs quantum dots are grown by means of molecular beam epitaxy on an InP substrate and are embedded into a quaternary In0.53Al0.23Ga0.24As membrane structure. In a post‐growth flip‐chip process with subsequent substrate removal and electron beam‐lithography, circular Bragg grating ("bullseye") resonators are defined. Micro‐photoluminescence studies of the devices at cryogenic temperatures of T=5$T = 5$ K reveal individual quantum dot emission lines into a pronounced cavity mode. Time‐correlated single‐photon counting measurements under above‐band gap excitation yield Purcell‐enhanced excitonic decay times of τ=(180±3)$\tau =(180\pm 3)$ ps corresponding to a Purcell factor of FP=(6.7±0.6)${F}_{P}=(6.7\pm 0.6)$. Pronounced photon antibunching with a background limited g(2)(0)=(0.057±0.004)${g}^{(2)}(0)=(0.057\pm 0.004)$ is observed, which demonstrates that the light originated mostly from one single quantum dot. [ABSTRACT FROM AUTHOR]

Generating single photons in the telecommunication wavelength range from semiconductor quantum dots (QDs) and interfacing them with spins of electrons or holes is of high interest in recent years, with research mainly focusing on indium‐based QDs. However, there is not much data on the optical and spin properties of gallium antimonide (GaSb) QDs, despite it being a physically rich system with an indirect to direct bandgap crossover in the telecom wavelength range. This work investigates the (quantum‐) optical properties of GaSb QDs, which are fabricated by filling droplet‐etched nanoholes in an aluminum gallium antimonide (AlGaSb) matrix. Photoluminescence (PL) features from isolated and highly symmetric QDs are observed that exhibit narrow linewidth in the telecom S‐band and show an excitonic fine structure splitting of up to ΔEFSS=(12.0±0.5)$\mathrm{\Delta}{\mathrm{E}}_{\mathrm{FSS}}= (12.0 \pm 0.5)$ µeV. Moreover, time‐resolved measurements of the decay characteristics of an exciton are performed and the second‐order photon autocorrelation function of the charge complex is measured to g2(0)=0.16±0.02${{\mathrm{g}}}^{\mathrm{2}}{\mathrm{(0)}} = 0.16 \pm 0.02$, revealing clear antibunching and thus proving the capability of this material platform to generate non‐classical light. [ABSTRACT FROM AUTHOR]

This article, published in Advanced Quantum Technologies, discusses the fabrication and investigation of strain-free gallium-antimonide (GaSb) quantum dots as single-photon sources in the telecom S-Band. The researchers used local droplet etching and nanohole infilling to create the quantum dots and conducted time-resolved photoluminescence and second-order autocorrelation measurements to analyze their optical properties. The results showed antibunching, indicating the potential of this material platform for generating non-classical light in the telecom range. The article provides more detailed information on this topic. [Extracted from the article]

Neuronal activity sculpts brain development by inducing the transcription of genes such as brain-derived neurotrophic factor ( Bdnf) that modulate the function of synapses. Sensory experience is transduced into changes in gene transcription via the activation of calcium signaling pathways downstream of both L-type voltage-gated calcium channels (L- VGCCs) and NMDA-type glutamate receptors ( NMDARs). These signaling pathways converge on the regulation of transcription factors including calcium-response factor (Ca RF). Although Ca RF is dispensable for the transcriptional induction of Bdnf following the activation of L- VGCCs, here we show that the loss of Ca RF leads to enhanced NMDAR-dependent transcription of Bdnf as well as Arc. We identify the NMDAR subunit-encoding gene Grin3a as a regulatory target of Ca RF, and we show that expression of both Carf and Grin3a is depressed by the elevation of intracellular calcium, linking the function of this transcriptional regulatory pathway to neuronal activity. We find that light-dependent activation of Bdnf and Arc transcription is enhanced in the visual cortex of young Ca RF knockout mice, suggesting a role for Ca RF-dependent dampening of NMDAR-dependent transcription in the developing brain. Finally, we demonstrate that enhanced Bdnf expression in Ca RF-lacking neurons increases inhibitory synapse formation. Taken together, these data reveal a novel role for Ca RF as an upstream regulator of NMDAR-dependent gene transcription and synapse formation in the developing brain. [ABSTRACT FROM AUTHOR]

ABSTRACT Based on quantitative cluster analyses of 52 constitutively expressed or behaviorally regulated genes in 23 brain regions, we present a global view of telencephalic organization of birds. The patterns of constitutively expressed genes revealed a partial mirror image organization of three major cell populations that wrap above, around, and below the ventricle and adjacent lamina through the mesopallium. The patterns of behaviorally regulated genes revealed functional columns of activation across boundaries of these cell populations, reminiscent of columns through layers of the mammalian cortex. The avian functionally regulated columns were of two types: those above the ventricle and associated mesopallial lamina, formed by our revised dorsal mesopallium, hyperpallium, and intercalated hyperpallium; and those below the ventricle, formed by our revised ventral mesopallium, nidopallium, and intercalated nidopallium. Based on these findings and known connectivity, we propose that the avian pallium has four major cell populations similar to those in mammalian cortex and some parts of the amygdala: 1) a primary sensory input population (intercalated pallium); 2) a secondary intrapallial population (nidopallium/hyperpallium); 3) a tertiary intrapallial population (mesopallium); and 4) a quaternary output population (the arcopallium). Each population contributes portions to columns that control different sensory or motor systems. We suggest that this organization of cell groups forms by expansion of contiguous developmental cell domains that wrap around the lateral ventricle and its extension through the middle of the mesopallium. We believe that the position of the lateral ventricle and its associated mesopallium lamina has resulted in a conceptual barrier to recognizing related cell groups across its border, thereby confounding our understanding of homologies with mammals. J. Comp. Neurol. 521:3614-3665, 2013. © 2013 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

ABSTRACT In our companion study (Jarvis et al. [2013] J Comp Neurol. doi: 10.1002/cne.23404) we used quantitative brain molecular profiling to discover that distinct subdivisions in the avian pallium above and below the ventricle and the associated mesopallium lamina have similar molecular profiles, leading to a hypothesis that they may form as continuous subdivisions around the lateral ventricle. To explore this hypothesis, here we profiled the expression of 16 genes at eight developmental stages. The genes included those that define brain subdivisions in the adult and some that are also involved in brain development. We found that phyletic hierarchical cluster and linear regression network analyses of gene expression profiles implicated single and mixed ancestry of these brain regions at early embryonic stages. Most gene expression-defined pallial subdivisions began as one ventral or dorsal domain that later formed specific folds around the lateral ventricle. Subsequently a clear ventricle boundary formed, partitioning them into dorsal and ventral pallial subdivisions surrounding the mesopallium lamina. These subdivisions each included two parts of the mesopallium, the nidopallium and hyperpallium, and the arcopallium and hippocampus, respectively. Each subdivision expression profile had a different temporal order of appearance, similar in timing to the order of analogous cell types of the mammalian cortex. Furthermore, like the mammalian pallium, expression in the ventral pallial subdivisions became distinct during prehatch development, whereas the dorsal portions did so during posthatch development. These findings support the continuum hypothesis of avian brain subdivision development around the ventricle and influence hypotheses on homologies of the avian pallium with other vertebrates. J. Comp. Neurol. 521:3666-3701, 2013. © 2013 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Mid‐infrared (MIR) resonant tunneling diode (RTD) photodetectors based on a p‐type doped AlAsSb/GaSb double‐barrier quantum well (DBQW) are proposed and investigated for their optoelectronic transport properties. At room temperature, a distinct resonant tunneling current with a region of negative differential conductance is measured. The peak‐to‐valley current ratio (PVCR) is 1.51. To provide photosensitivity within the MIR spectral region, a lattice‐matched quaternary low‐bandgap GaInAsSb absorption layer with cutoff wavelength of λ = 2.77 μm is integrated near the DBQW. Under illumination with infrared light, photogenerated minority electrons within the absorption layer can drift toward the DBQW, where they accumulate and cause a shift of the current–voltage characteristics toward smaller bias voltages, which can be exploited to measure the incident MIR light power. In a tunable diode laser absorption spectroscopy experiment, the RTD photodetector is used to identify three distinct water absorption lines in the MIR close to λ = 2.61 μm. By adjusting the absorption layer doping concentration, the RTD quantum efficiency can be increased by a factor of 10, resulting in a sensitivity of S = 2.71 A W−1, which corresponds to an estimated multiplication factor of M = 8.6. Antimony‐based resonant tunneling diodes (RTDs) are a promising alternative for mid‐infrared (MIR) photodetectors with gain at considerably low operation voltages. Their capability is demonstrated in a tunable diode laser absorption spectroscopy (TDLAS) experiment. The possibility to exploit hole transport by p‐type doping provides further advantages and can also be applied to alternative material systems such as GaAs or InP. [ABSTRACT FROM AUTHOR]