Social media has arguably shifted political agenda-setting power away from mainstream media onto politicians. Current U.S. President Trump's reliance on Twitter is unprecedented, but the underlying ...implications for agenda setting are poorly understood. Using the president as a case study, we present evidence suggesting that President Trump's use of Twitter diverts crucial media (The New York Times and ABC News) from topics that are potentially harmful to him. We find that increased media coverage of the Mueller investigation is immediately followed by Trump tweeting increasingly about unrelated issues. This increased activity, in turn, is followed by a reduction in coverage of the Mueller investigation-a finding that is consistent with the hypothesis that President Trump's tweets may also successfully divert the media from topics that he considers threatening. The pattern is absent in placebo analyses involving Brexit coverage and several other topics that do not present a political risk to the president. Our results are robust to the inclusion of numerous control variables and examination of several alternative explanations, although the generality of the successful diversion must be established by further investigation.
Efficient fibre-based long-distance quantum communication via quantum repeaters relies on deterministic single-photon sources at telecom wavelengths, potentially exploiting the existing world-wide ...infrastructures. For upscaling the experimental complexity in quantum networking, two-photon interference (TPI) of remote non-classical emitters in the low-loss telecom bands is of utmost importance. Several experiments have been conducted regarding TPI of distinct emitters, for example, using trapped atoms
, ions
, nitrogen vacancy centres
, silicon vacancy centres
, organic molecules
and semiconductor quantum dots
. However, the spectral range was far from the highly desirable telecom C-band. Here, we exploit quantum frequency conversion to realize TPI at 1,550 nm with single photons stemming from two remote quantum dots. We thereby prove quantum frequency conversion
as a bridging technology and a precise and stable mechanism to erase the frequency difference between independent emitters. On resonance, a TPI visibility of 29 ± 3% has been observed, limited only by the spectral diffusion processes of the individual quantum dots
. The local fibre network used covers several rooms between two floors of the building. Even the addition of up to 2 km of fibre channel shows no influence on the TPI visibility, proving the photon wavepacket distortion to be negligible. Our studies pave the way to establish long-distance entanglement distribution between remote solid-state emitters including interfaces with various quantum hybrid systems
.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
This paper tests for a causal connection between media attention devoted to terrorism and subsequent attacks. Analyzing 61,132 attack days in 201 countries produces evidence that increased New York ...Times coverage encourages further attacks in the same country. Using natural disasters in the United States as an exogenous variation diminishing media attention, the link appears causal. One additional article is suggested to produce 1.4 attacks over the following week, equivalent to three casualties on average. This result is robust to numerous alternative estimations and it appears unlikely that attacks are simply postponed. If terrorists do not receive media attention, they will attack less.
•Analyzing NYT coverage of 61,132 terrorist attack days in 201 countries and 43years•Testing for a causal effect of media coverage of terrorism on subsequent attacks•Natural disasters in the US provide an IV that exogenously diminishes media coverage.•IV results show strong positive effect.•1 NYT article translates to 1.4 attacks in following week or 3 casualties.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Solid-state quantum emitters with manipulable spin-qubits are promising platforms for quantum communication applications. Although such light-matter interfaces could be realized in many systems only ...a few allow for light emission in the telecom bands necessary for long-distance quantum networks. Here, we propose and implement an optically active solid-state spin-qubit based on a hole confined in a single InAs/GaAs quantum dot grown on an InGaAs metamorphic buffer layer emitting photons in the C-band. We lift the hole spin-degeneracy using an external magnetic field and demonstrate hole injection, initialization, read-out and complete coherent control using picosecond optical pulses. These results showcase a solid-state spin-qubit platform compatible with preexisting optical fiber networks.
Quantum mechanics promises to have a strong impact on many aspects of research and technology, improving classical analogues via purely quantum effects. A large variety of tasks are currently under ...investigation, for example, the implementation of quantum computing, sensing, metrology, and communication. From a general perspective, in a similar way as classical computing benefited by the reduction of the device footprint, enabling the realization of highly complex chips, a range of quantum applications will sensibly improve thanks to the successful realization of on‐chip quantum photonics. Conversely to bulky table‐top experiments, it would be very advantageous to transfer all required functionalities on the same quantum photonic chip. The key elements for quantum photonic circuits are on‐demand nonclassical light sources, a versatile photonic logic, the ability to store quantum information, and highly efficient detectors, directly integrated on‐chip. Among several systems capable of the efficient generation of single‐ and indistinguishable photons, quantum dots are rapidly establishing as one of the most appealing candidates. This paper reviews the recent progress in the on‐chip integration of quantum‐dot‐based nonclassical light sources as well as in the development of the main building blocks, either integrated monolithically or hybridly on a compact and scalable platform.
Semiconductor quantum dots are rapidly establishing as one of the most appealing candidates for the efficient generation of nonclassical photons. This review highlights the recent progress in the on‐chip integration of quantum‐dot‐based nonclassical light sources as well as in the development of the main building blocks for the realization of a compact and scalable quantum photonic platform.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Abstract
Hybrid quantum systems integrating semiconductor quantum dots (QDs) and atomic vapours become important building blocks for scalable quantum networks due to the complementary strengths of ...individual parts. QDs provide on-demand single-photon emission with near-unity indistinguishability comprising unprecedented brightness—while atomic vapour systems provide ultra-precise frequency standards and promise long coherence times for the storage of qubits. Spectral filtering is one of the key components for the successful link between QD photons and atoms. Here we present a tailored Faraday anomalous dispersion optical filter based on the caesium-D
1
transition for interfacing it with a resonantly pumped QD. The presented Faraday filter enables a narrow-bandwidth (Δ
ω
=2
π
× 1 GHz) simultaneous filtering of both Mollow triplet sidebands. This result opens the way to use QDs as sources of single as well as cascaded photons in photonic quantum networks aligned to the primary frequency standard of the caesium clock transition.
This paper explores the consequences of al-Qaeda news coverage related to (i) subsequent al-Qaeda attacks, (ii) the group’s popularity, and (iii) radicalization. I construct a daily index of al-Qaeda ...news coverage in the US from CNN, NBC, CBS, Fox News, the NYT, and the WaPo. To isolate causality, I employ an instrumental variable strategy based on disaster deaths: Everything else equal, the US media reports less on al-Qaeda when more people are dying from disasters worldwide. At its mean, al-Qaeda coverage is suggested to cause 0.2–0.3 attacks per day in the upcoming 1–4 weeks. I find no evidence that attacks are merely rescheduled because of diminished media exposure; rather, the total number of attacks increases with coverage. This effect is driven by easy-to-plan attack types and by al-Qaeda attacks in Iraq. Results are robust to an array of alternative specifications and consistent when considering news coverage on Al Jazeera. Al-Qaeda coverage also increases the group’s online popularity and search topics that are potentially indicative of radicalization (such as jihad and al-Qaeda’s magazine Inspire) are receiving more attention on Google. Nevertheless, these results should be interpreted carefully, as it remains difficult to fully disentangle online interest in al-Qaeda and sympathy with the group’s mission.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
A key challenge in quantum photonics today is the efficient and on-demand generation of high-quality single photons and entangled photon pairs. In this regard, one of the most promising types of ...emitters are semiconductor quantum dots, fluorescent nanostructures also described as artificial atoms. The main technological challenge in upscaling to an industrial level is the typically random spatial and spectral distribution in their growth. Furthermore, depending on the intended application, different requirements are imposed on a quantum dot, which are reflected in its spectral properties. Given that an in-depth suitability analysis is lengthy and costly, it is common practice to pre-select promising candidate quantum dots using their emission spectrum. Currently, this is done by hand. Therefore, to automate and expedite this process, in this paper, we propose a data-driven machine-learning-based method of evaluating the applicability of a semiconductor quantum dot as single photon source. For this, first, a minimally redundant, but maximally relevant feature representation for quantum dot emission spectra is derived by combining conventional spectral analysis with an autoencoding convolutional neural network. The obtained feature vector is subsequently used as input to a neural network regression model, which is specifically designed to not only return a rating score, gauging the technical suitability of a quantum dot, but also a measure of confidence for its evaluation. For training and testing, a large dataset of self-assembled InAs/GaAs semiconductor quantum dot emission spectra is used, partially labelled by a team of experts in the field. Overall, highly convincing results are achieved, as quantum dots are reliably evaluated correctly. Note, that the presented methodology can account for different spectral requirements and is applicable regardless of the underlying photonic structure, fabrication method and material composition. We therefore consider it the first step towards a fully integrated evaluation framework for quantum dots, proving the use of machine learning beneficial in the advancement of future quantum technologies.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Abstract
Atomically thin layered van der Waals heterostructures feature exotic and emergent optoelectronic properties. With growing interest in these novel quantum materials, the microscopic ...understanding of fundamental interfacial coupling mechanisms is of capital importance. Here, using multidimensional photoemission spectroscopy, we provide a layer- and momentum-resolved view on ultrafast interlayer electron and energy transfer in a monolayer-WSe
2
/graphene heterostructure. Depending on the nature of the optically prepared state, we find the different dominating transfer mechanisms: while electron injection from graphene to WSe
2
is observed after photoexcitation of quasi-free hot carriers in the graphene layer, we establish an interfacial Meitner-Auger energy transfer process following the excitation of excitons in WSe
2
. By analysing the time-energy-momentum distributions of excited-state carriers with a rate-equation model, we distinguish these two types of interfacial dynamics and identify the ultrafast conversion of excitons in WSe
2
to valence band transitions in graphene. Microscopic calculations find interfacial dipole-monopole coupling underlying the Meitner-Auger energy transfer to dominate over conventional Förster- and Dexter-type interactions, in agreement with the experimental observations. The energy transfer mechanism revealed here might enable new hot-carrier-based device concepts with van der Waals heterostructures.
This article introduces a simple game-theoretic model to explain how policymakers' decisions may result in underinvestment in the global space sector. Because of international spillovers, ...policymakers can arrive at a globally suboptimal Nash equilibrium. We then show that policymakers may achieve optimal outcomes by focussing on international, rather than domestic space projects. Next, we introduce time dynamics to enhance the model's realism and show that improving quantitative cost-benefit analysis methods may further remedy underinvestment, as policymakers can overcome the influence of international spillovers and reach the optimal outcome by assigning higher values to future payoffs. However, when we modify the traditional iterated prisoner's dilemma to more accurately represent space sector funding dynamics, we find further evidence for a propensity to underinvest. As such, we show that the dynamic game solution is imperfect: democratic policymakers are inherently constrained by electoral cycles and future payoffs from space programs that tend to be difficult to predict, especially when compared to more traditional public policy programs. We recommend that governments should support private companies in the space sector to benefit from the comparative advantages they offer.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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