Atomically-thin single-photon sources for quantum communication

To date, quantum communication widely relies on attenuated lasers for secret key generation. In future quantum networks, fundamental limitations resulting from their probabilistic photon distribution must be overcome by using deterministic quantum light sources. Confined excitons in monolayers of transition metal dichalcogenides (TMDCs) constitute an emerging type of emitter for quantum light generation. These atomically thin solid-state sources show appealing prospects for large-scale and low-cost device integration, meeting the demands of quantum information technologies. Here, we pioneer the practical suitability of TMDC devices in quantum communication. We employ a WSe2 monolayer single-photon source to emulate the BB84 protocol in a quantum key distribution (QKD) setup and achieve click rates of up to 66.95 kHz and antibunching values down to 0.034—a performance competitive with QKD experiments using semiconductor quantum dots or color centers in diamond. Our work opens the route towards wider applications of quantum information technologies using TMDC single-photon source

Development of site-controlled quantum dot arrays acting as scalable sources of indistinguishable photons

We report on the realization of an array of 28 × 28 mesas with site-controlled InGaAs quantum dots acting as single-photon sources for potential applications in photonic quantum technology. The site-selective growth of quantum dots is achieved by using the buried stressor approach where an oxide aperture serves as the nucleation site in the center of each mesa. Spectroscopic maps demonstrate the positioning of quantum dots with an inhomogeneous broadening of the ensemble emission of only 15.8 meV. Individual quantum dots are characterized by clean single-quantum-dot spectra with narrow exciton, biexciton, and trion lines, with a best value of 27 μeV and an ensemble average of 120 μeV. Beyond that, Hanbury Brown and Twiss and Hong-Ou-Mandel measurements validate the quantum nature of emission in terms of high single-photon purity and photon indistinguishability with a g(2)(0) value of (0.026 ± 0.026) and a post-selected two-photon interference visibility V = (87.1 ± 9.7)% with an associated coherence time of τc = (194 ± 7) ps.DFG, 43659573, SFB 787: Semiconductor Nanophotonics: Materials, Models, Device

Exploring the photon-number distribution of bimodal microlasers with a transition edge sensor

The research leading to these results has received funding from the European Research Council under the European Union's Seventh Framework ERC Grant Agreement No. 615613, within the EURAMET joint research project MIQC2 from the European Union's Horizon 2020 Research and Innovation Programme and the EMPIR Participating States and from the German Research Foundation within the project RE2974/10-1. The authors thank the State of Bavaria for financial support.A photon-number resolving transition edge sensor (TES) is used to measure the photon-number distribution of two microcavity lasers. The investigated devices are bimodal microlasers with similar emission intensity and photon statistics with respect to the photon auto-correlation. Both high-β microlasers show partly thermal and partly coherent emission around the lasing threshold. For higher pump powers, the strong mode of microlaser { A } emits Poissonian distributed photons while the emission of the weak mode is thermal. In contrast, laser { B } shows a bistability resulting in overlayed thermal and Poissonian distributions. While a standard Hanbury Brown and Twiss experiment cannot distinguish between simple thermal emission of laser { A } and the temporal mode switching of the bistable laser { B }, TESs allow us to measure the photon-number distribution which provides important insight into the underlying emission processes. Indeed, our experimental data and its theoretical description by a master equation approach show that TESs are capable of revealing subtle effects like mode switching of bimodal microlasers. As such our studies clearly demonstrate the benefit and importance of investigating nanophotonic devices via photon-number resolving transition edge sensors.PostprintPeer reviewe

Temperature dependent temporal coherence of metallic-nanoparticle-induced single-photon emitters in a WSe2_{2} monolayer

In recent years, much research has been undertaken to investigate the suitability of two-dimensional materials to act as single-photon sources with high optical and quantum optical quality. Amongst them, transition-metal dichalcogenides, especially WSe$_{2}$, have been one of the subjects of intensive studies. Yet, their single-photon purity and photon indistinguishability, remain the most significant challenges to compete with mature semiconducting systems such as self-assembled InGaAs quantum dots. In this work, we explore the emission properties of quantum emitters in a WSe$_{2}$ monolayer which are induced by metallic nanoparticles. Under quasi-resonant pulsed excitation, we verify clean single-photon emission with a $g^{(2)}(0) = 0.036\pm0.004$. Furthermore, we determine its temperature dependent coherence time via Michelson interferometry, where a value of (13.5$\pm$1.0) ps is extracted for the zero-phonon line (ZPL) at 4 K, which reduces to (9$\pm$2) ps at 8 K. Associated time-resolved photoluminescence experiments reveal a decrease of the decay time from (2.4$\pm$0.1) ns to (0.42$\pm$0.05) ns. This change in decay time is explained by a model which considers a F\"orster-type resonant energy transfer process, which yields a strong temperature induced energy loss from the SPE to the nearby Ag nanoparticle

Scalable deterministic integration of two quantum dots into an on-chip quantum circuit

Integrated quantum photonic circuits (IQPCs) with deterministically integrated quantum emitters are critical elements for scalable quantum information applications and have attracted significant attention in recent years. However, scaling up them towards fully functional photonic circuits with multiple deterministically integrated quantum emitters to generate photonic input states remains a great challenge. In this work, we report on a monolithic prototype IQPC consisting of two pre-selected quantum dots deterministically integrated into nanobeam cavities at the input ports of a 2x2 multimode interference beam-splitter. The on-chip beam splitter exhibits a splitting ratio of nearly 50/50 and the integrated quantum emitters have high single-photon purity, enabling on-chip HBT experiments, depicting deterministic scalability. Overall, this marks a cornerstone toward scalable and fully-functional IQPCs

Tailoring the mode-switching dynamics in quantum-dot micropillar lasers via time-delayed optical feedback

Funding: European Research Council under the European Union’s Seventh Framework Program (ERC Grant Agreement No. 615613); German Research Foundation (CRC 787, GRK1558); project EMPIR 14IND05 MIQC2 co-financed by the Participating States and from the European Union’s Horizon 2020 research and innovation program.Microlasers are ideal candidates to bring the fascinating variety of nonlinear complex dynamics found in delay-coupled systems to the realm of quantum optics. Particularly attractive is the possibility of tailoring the devices’ emission properties via non-invasive delayed optical coupling. However, until now scarce research has been done in this direction. Here, we experimentally and theoretically investigate the effects of delayed optical feedback on the mode-switching dynamics of an electrically driven bimodal quantum-dot micropillar laser, characterizing its impact on the micropillar’s output power, optical spectrum and photon statistics. Feedback is found to influence the switching dynamics and its characteristics time scales. In addition, stochastic switching is reduced with the subsequent impact on the microlaser photon statistics. Our results contribute to the comprehension of feedback-induced phenomena in micropillar lasers and pave the way towards the external control and tailoring of the properties of these key systems for the nanophotonics community.Publisher PDFPeer reviewe

Neuronal precision and the limits for acoustic signal recognition in a small neuronal network

Recognition of acoustic signals may be impeded by two factors: extrinsic noise, which degrades sounds before they arrive at the receiver’s ears, and intrinsic neuronal noise, which reveals itself in the trial-to-trial variability of the responses to identical sounds. Here we analyzed how these two noise sources affect the recognition of acoustic signals from potential mates in grasshoppers. By progressively corrupting the envelope of a female song, we determined the critical degradation level at which males failed to recognize a courtship call in behavioral experiments. Using the same stimuli, we recorded intracellularly from auditory neurons at three different processing levels, and quantified the corresponding changes in spike train patterns by a spike train metric, which assigns a distance between spike trains. Unexpectedly, for most neurons, intrinsic variability accounted for the main part of the metric distance between spike trains, even at the strongest degradation levels. At consecutive levels of processing, intrinsic variability increased, while the sensitivity to external noise decreased. We followed two approaches to determine critical degradation levels from spike train dissimilarities, and compared the results with the limits of signal recognition measured in behaving animals

Quantum light sources based on deterministic microlenses structures with (111) In(Ga)As and AlInAs QDs.

The results of the development and implementation of a single photon source based on a bottom semiconductor Bragg reflector, top deterministic GaAs microlens structures and a single (111) In(Ga)As QD are presented. The structure of the microcavity ensures effective pumping of a single (111) In(Ga)As QD and high emission output efficiency, a clear single – photon emission was detected with a second – order correlation function at zero delay g(2)(0) = 0.07. A system of QD’s on the basis of AlXIn1-XAs/AlYGa1-YAs solid solutions has been studied. The usage of broadband AlXIn1-XAs solid solutions as the basis of quantum dots makes it possible to expand considerably the spectral emission range into the short-wave region, including the wavelength region near 770 nm being of interest for the design of aerospace systems of quantum cryptography. The optical characteristics of single AlXIn1-XAs quantum dots grown according to the Stranski–Krastanov mechanism are studied by the cryogenic microphotoluminescence method

Toxic but Drank: Gustatory Aversive Compounds Induce Post-ingestional Malaise in Harnessed Honeybees

BACKGROUND: Deterrent substances produced by plants are relevant due to their potential toxicity. The fact that most of these substances have an unpalatable taste for humans and other mammals contrasts with the fact that honeybees do not reject them in the range of concentrations in which these compounds are present in flower nectars. Here we asked whether honeybees detect and ingest deterrent substances and whether these substances are really toxic to them. RESULTS: We show that pairing aversive substances with an odor retards learning of this odor when it is subsequently paired with sucrose. Harnessed honeybees in the laboratory ingest without reluctance a considerable volume (20 µl) of various aversive substances, even if some of them induce significant post-ingestional mortality. These substances do not seem, therefore, to be unpalatable to harnessed bees but induce a malaise-like state that in some cases results in death. Consistently with this finding, bees learning that one odor is associated with sugar, and experiencing in a subsequent phase that the sugar was paired with 20 µl of an aversive substance (devaluation phase), respond less than control bees to the odor and the sugar. Such stimulus devaluation can be accounted for by the malaise-like state induced by the aversive substances. CONCLUSION: Our results indicate that substances that taste bitter to humans as well as concentrated saline solutions base their aversive effect on the physiological consequences that their ingestion generates in harnessed bees rather than on an unpalatable taste. This conclusion is only valid for harnessed bees in the laboratory as freely-moving bees might react differently to aversive compounds could actively reject aversive substances. Our results open a new possibility to study conditioned taste aversion based on post-ingestional malaise and thus broaden the spectrum of aversive learning protocols available in honeybees

Crowdsourcing hypothesis tests: Making transparent how design choices shape research results

To what extent are research results influenced by subjective decisions that scientists make as they design studies? Fifteen research teams independently designed studies to answer fiveoriginal research questions related to moral judgments, negotiations, and implicit cognition. Participants from two separate large samples (total N > 15,000) were then randomly assigned to complete one version of each study. Effect sizes varied dramatically across different sets of materials designed to test the same hypothesis: materials from different teams renderedstatistically significant effects in opposite directions for four out of five hypotheses, with the narrowest range in estimates being d = -0.37 to +0.26. Meta-analysis and a Bayesian perspective on the results revealed overall support for two hypotheses, and a lack of support for three hypotheses. Overall, practically none of the variability in effect sizes was attributable to the skill of the research team in designing materials, while considerable variability was attributable to the hypothesis being tested. In a forecasting survey, predictions of other scientists were significantly correlated with study results, both across and within hypotheses. Crowdsourced testing of research hypotheses helps reveal the true consistency of empirical support for a scientific claim.</div