Efficient demultiplexed single-photon source with a quantum dot coupled to a nanophotonic waveguide

Planar nanostructures allow near-ideal extraction of emission from a quantum emitter embedded within, thereby realizing deterministic single-photon sources. Such a source can be transformed into M single-photon sources by implementing active temporal-to-spatial mode demultiplexing. We report on the realization of such a demultiplexed source based on a quantum dot embedded in a nanophotonic waveguide. Efficient outcoupling (>60%) from the waveguide into a single mode optical fiber is obtained with high-efficiency grating couplers. As a proof-of-concept, active demultiplexing into M=4 spatial channels is demonstrated by the use of electro-optic modulators with an end-to-end efficiency of >81% into single-mode fibers. Overall we demonstrate four-photon coincidence rates of >1 Hz even under non-resonant excitation of the quantum dot. The main limitation of the current source is the residual population of other exciton transitions that corresponds to a finite preparation efficiency of the desired transition. We quantitatively extract a preparation efficiency of 15% using the second-order correlation function measurements. The experiment highlights the applicability of planar nanostructures as efficient multiphoton sources through temporal-to-spatial demultiplexing and lays out a clear path way of how to scale up towards demonstrating quantum advantages with the quantum dot sources.Comment: 5 pages, 3 figure

Size-Dependence of the Wavefunction of Self-Assembled Quantum Dots

The radiative and non-radiative decay rates of InAs quantum dots are measured by controlling the local density of optical states near an interface. From time-resolved measurements we extract the oscillator strength and the quantum efficiency and their dependence on emission energy. From our results and a theoretical model we determine the striking dependence of the overlap of the electron and hole wavefunctions on the quantum dot size. We conclude that the optical quality is best for large quantum dots, which is important in order to optimally tailor quantum dot emitters for, e.g., quantum electrodynamics experiments.Comment: 5 pages, 3 figure

Ischemic Heart Disease in Chronic Hepatitis B: A Danish Nationwide Cohort Study

OBJECTIVE: Data on the risk of ischemic heart disease (IHD) in patients with chronic hepatitis B virus (CHB) are conflicting. Our objective was to address the rate of IHD in patients with CHB compared with individuals without CHB (control-persons) from the general population. STUDY DESIGN AND SETTING: We conducted a cohort study of prospectively obtained data from Danish nationwide registries. We produced cumulative incidence curves and calculated the unadjusted incidence rate ratio (IRR) of IHD in persons with and without CHB. The adjusted association between having CHB and developing IHD was examined using a cause-specific Cox regression model. RESULTS: In total, 6472 persons with CHB and 62,251 age- and sex-matched individuals from the general population were followed for 48,840 and 567,456 person-years, respectively, during which 103 (1,59%) with CHB and 1058 (1,70%) control-persons developed IHD. The crude IRR was 1.13 (95% CI: 0.91–1.39). CHB did not have a statistically significant effect on the rate of IHD after adjusting for several confounding factors (adjusted hazard ratio: 0.96, 95% CI: 0.76–1.21). CONCLUSION: In this nationwide cohort study, we did not find any difference between rate of IHD in persons with CHB in comparison with the general population

The Influence of Entry Mode and Distribution Strategies on Transportation Route Selection of Japanese Electronics Manufacturers in Russia

Objectives of the Research The purpose of this research is to study the entry mode strategies of Japanese electronics manufacturers entering the Russian market and how the entry mode strategy influences the distribution strategy and the transportation route selection. Additionally the objective is to examine what other factors influence the choice of transportation route to Russia, and what are the benefits of using one route over the other. In the study three routes of the Baltic Sea are compared: Finland, the Baltic countries and St. Petersburg. Methodology The research is a qualitative single case study. Structured interviews were used for data collection, as well as other materials provided by the company and found on the company web pages. Data collection and analysis were done around the themes of market entry modes, distribution strategy and transport route selection. Findings and Conclusions The main findings of this thesis suggest that the entry mode strategies of companies operating in Russia have developed over time from non-equity to equity entry modes. Companies are finding the environment more suitable for FDI and are therefore establishing sales subsidiaries in the country. The institutional environment of Russia affects the entry modes as the factors affecting the strategies may not be the same as in the western countries. The distribution strategy closely follows the entry mode strategy, and needs to be developed as the entry mode strategy changes. Both of these strategies are guided by the tradeoffs between costs and services as well as efficiency and responsiveness. As the companies decide on an appropriate strategy, the transportation route is selected to support this strategy. Routes that offer better lead times can present companies a change to have better customer service, however reliability needs to be also considered to ensure product availability. On top of these, the costs are also important factors companies consider when selecting the most suitable transportation route. Key words Entry mode strategy, distribution strategy, transit traffic, gateway, Russia, transportation route