Coherence and indistinguishability of highly pure single photons from non-resonantly and resonantly excited telecom C-band quantum dots

In the present work, the effect of resonant pumping schemes in improving the photon coherence is investigated on InAs/InGaAs/GaAs quantum dots emitting in the telecom C-band. The linewidths of transitions of multiple exemplary quantum dots are determined under above-band pumping and resonance fluorescence via Fourier-transform spectroscopy and resonance scans, respectively. The average linewidth is reduced from $9.74\,\mathrm{GHz}$ in above-band excitation to $3.50\,\mathrm{GHz}$ in resonance fluorescence underlining its superior coherence properties. Furthermore, the feasibility of coherent state preparation with a fidelity of $49.2\,\%$ is demonstrated, constituting a step towards on-demand generation of coherent, single C-band photons from quantum dots. Finally, two-photon excitation of the biexciton is investigated as a resonant pumping scheme. A deconvoluted single-photon purity value of $g^{(2)}_{\mathrm{HBT}}(0)=0.072\pm 0.104$ and a degree of indistinguishability of $V_{\mathrm{HOM}}=0.894\pm0.109$ are determined for the biexciton transition. This represents an important step towards fulfilling the prerequisites for quantum communication applications like quantum repeater schemes at telecom wavelength

Distinguishing Direct from Indirect Interactions in Oscillatory Networks with Multiple Time Scales

Peer reviewedPublisher PD

An Arabidopsis flavonoid transporter is required for anther dehiscence and pollen development

FLOWER FLAVONOID TRANSPORTER (FFT) encodes a multidrug and toxin efflux family transporter in Arabidopsis thaliana. FFT (AtDTX35) is highly transcribed in floral tissues, the transcript being localized to epidermal guard cells, including those of the anthers, stigma, siliques and nectaries. Mutant analysis demonstrates that the absence of FFT transcript affects flavonoid levels in the plant and that the altered flavonoid metabolism has wide-ranging consequences. Root growth, seed development and germination, and pollen development, release and viability are all affected. Spectrometry of mutant versus wild-type flowers shows altered levels of a glycosylated flavonol whereas anthocyanin seems unlikely to be the substrate as previously speculated. Thus, as well as adding FFT to the incompletely described flavonoid transport network, it is found that correct reproductive development in Arabidopsis is perturbed when this particular transporter is missing

The biochemical properties of the two <i>Arabidopsis thaliana</i> isochorismate synthases

The important plant hormone salicylic acid (SA; 2-hydroxybenzoic acid) regulates several key plant responses including, most notably, defence against pathogens. A key enzyme for SA biosynthesis is isochorismate synthase (ICS), which converts chorismate to isochorismate, for which there are two genes in Arabidopsis thaliana . One ( AtICS1 ) has been shown to be required for increased SA biosynthesis in response to pathogens and its expression can be stimulated throughout the leaf by virus infection and exogenous SA. The other ( AtICS2 ) appears to be expressed constitutively, predominantly in the plant vasculature. Here, we characterise the enzymatic activity of both isozymes expressed as hexahistidine fusion proteins in Escherichia coli. We show for the first time that recombinant AtICS2 is enzymatically active. Both isozymes are Mg(2+)-dependent with similar temperature optima ( c. 33ºC) and similar Km values for chorismate of 34.3±3.7 and 28.8±6.9 mM for ICS1 and ICS2, respectively, but reaction rates were greater for ICS1 than for ICS2, with respective values for Vmax of 63.5±2.4 and 28.3±2.0 nM.s(-1) and for kcat of 38.1±1.5 and 17.0±1.2 min(-1). However, neither enzyme displayed isochorismate pyruvate lyase (IPL) activity, which would enable these proteins to act as bifunctional SA synthases, i.e. to convert chorismate to SA. These results show that although Arabidopsis has two functional ICS enzymes it must possess one or more IPL enzymes to complete biosynthesis of SA starting from chorismate.</p

NPR3 and NPR4 are receptors for the immune signal salicylic acid in plants

Salicylic acid (SA) is a plant immune signal produced upon pathogen challenge to induce systemic acquired resistance (SAR). It is the only major plant hormone for which the receptor has not been firmly identified. SAR in Arabidopsis requires the transcription cofactor NPR1 (nonexpresser of PR genes 1), whose degradation serves as a molecular switch for SAR. Here we show that NPR1 paralogues, NPR3 and NPR4, are SA receptors that bind SA with different affinities and function as adaptors of the Cullin 3 ubiquitin E3 ligase to mediate NPR1 degradation in an SA-regulated manner. Accordingly, the npr3 npr4 mutant accumulates higher levels of NPR1 and is insensitive to SAR induction. Moreover, this mutant is defective in pathogen effector-triggered programmed cell death and immunity. Our study reveals the mechanism of SA perception in determining cell death and survival in response to pathogen challenge

Non-equilibrium spin noise spectroscopy of a single quantum dot operating at fiber telecommunication wavelengths

We report on the spin and occupation noise of a single, positively charged (InGa)As quantum dot emitting photons in the telecommunication C-band. The spin noise spectroscopy measurements are carried out at a temperature of 4.2 K in dependence on intensity and detuning in the regime beyond thermal equilibrium. The spin noise spectra yield in combination with an elaborate theoretical model the hole-spin relaxation time of the positively charged quantum dot and the Auger recombination and the electron-spin relaxation time of the trion state. The extracted Auger recombination time of this quantum dot emitting at 1.55 μm is comparable to the typical Auger recombination times on the order of a few μs measured in traditionally grown InAs/GaAs quantum dots emitting at around 900 nm

Expression profiling during arabidopsis/downy mildew interaction reveals a highly-expressed effector that attenuates responses to salicylic acid

Plants have evolved strong innate immunity mechanisms, but successful pathogens evade or suppress plant immunity via effectors delivered into the plant cell. Hyaloperonospora arabidopsidis (Hpa) causes downy mildew on Arabidopsis thaliana, and a genome sequence is available for isolate Emoy2. Here, we exploit the availability of genome sequences for Hpa and Arabidopsis to measure gene-expression changes in both Hpa and Arabidopsis simultaneously during infection. Using a high-throughput cDNA tag sequencing method, we reveal expression patterns of Hpa predicted effectors and Arabidopsis genes in compatible and incompatible interactions, and promoter elements associated with Hpa genes expressed during infection. By resequencing Hpa isolate Waco9, we found it evades Arabidopsis resistance gene RPP1 through deletion of the cognate recognized effector ATR1. Arabidopsis salicylic acid (SA)-responsive genes including PR1 were activated not only at early time points in the incompatible interaction but also at late time points in the compatible interaction. By histochemical analysis, we found that Hpa suppresses SA-inducible PR1 expression, specifically in the haustoriated cells into which host-translocated effectors are delivered, but not in non-haustoriated adjacent cells. Finally, we found a highly-expressed Hpa effector candidate that suppresses responsiveness to SA. As this approach can be easily applied to host-pathogen interactions for which both host and pathogen genome sequences are available, this work opens the door towards transcriptome studies in infection biology that should help unravel pathogen infection strategies and the mechanisms by which host defense responses are overcome

BIO-WELL: The development and validation of a human wellbeing scale that measures responses to biodiversity

The evidence linking nature and human wellbeing is compelling. Yet, there is a lack of understanding regarding which aspects of nature contribute to wellbeing and the role biodiversity plays specifically. This knowledge gap hampers our ability to understand and manage natural environments from an ecological perspective to improve human wellbeing. To investigate the impact of biodiversity on wellbeing in a range of contexts, there is a need for a psychometric scale. Here, we present BIO-WELL, a novel, reliable and validated self-reported wellbeing scale designed to investigate the biodiversity-health/wellbeing relationship. We describe the conceptual foundation, empirical development and psychometric evaluation of BIO-WELL. We detail five studies, involving 2962 participants, describing the steps taken in the scale's development: (1) a series of deliberative workshops to identify how people conceptualise biodiversity metrics and attributes, and the impact these have on wellbeing; (2) an in-depth qualitative analysis of biodiversity-focused stem questions and wellbeing response items, assessed through an expert panel, focus groups and cognitive interviewing techniques; (3) combined methods associated with classical test theory (e.g. factor analysis) and more modern measurement approaches drawn from item response theory to develop the scale; (4) a confirmatory factor analysis alongside classical test and item response theories to evaluate the scale; and (5) scale validation including discriminant/convergent, concurrent and predictive. The studies demonstrate that BIO-WELL is a valid and reliable scale with strong psychometric properties. We discuss ways it could be applied in research, policy and practice to further develop our conceptual and empirical understanding of the biodiversity-health relationship and assess the effectiveness of related interventions

O-linked sialoglycans modulate the proteolysis of Sars-Cov-2 spike and likely contribute to the mutational trajectory in variants of concern

The emergence of a polybasic cleavage motif for the protease furin in SARS-CoV-2 spike has been established as a major factor for human viral transmission. The region N-terminal to that motif is extensively mutated in variants of concern (VOCs). Besides furin, spikes from these variants appear to rely on other proteases for maturation, including TMPRSS2. Glycans near the cleavage site have raised questions about proteolytic processing and the consequences of variant-borne mutations. Here, we identify that sialic acid-containing O-linked glycans on Thr678 of SARS-CoV-2 spike influence furin and TMPRSS2 cleavage and posit O-linked glycosylation as a likely driving force for the emergence of VOC mutations. We provide direct evidence that the glycosyltransferase GalNAc-T1 primes glycosylation at Thr678 in the living cell, an event that is suppressed by mutations in the VOCs Alpha, Delta, and Omicron. We found that the sole incorporation of N-acetylgalactosamine did not impact furin activity in synthetic O-glycopeptides, but the presence of sialic acid reduced the furin rate by up to 65%. Similarly, O-glycosylation with a sialylated trisaccharide had a negative impact on TMPRSS2 cleavage. With a chemistry-centered approach, we substantiate O-glycosylation as a major determinant of spike maturation and propose disruption of O-glycosylation as a substantial driving force for VOC evolution