193 research outputs found
Anticipated election result and protest voting: why and when Canadian voters signal discontent
Strain-Tunable GaAs Quantum dot: A Nearly Dephasing-Free Source of Entangled Photon Pairs on Demand
Entangled photon generation from semiconductor quantum dots via the
biexciton-exciton cascade underlies various decoherence mechanisms related to
the solid-state nature of the quantum emitters. So far, this has prevented the
demonstration of nearly-maximally entangled photons without the aid of
inefficient and complex post-selection techniques that are hardly suitable for
quantum communication technologies. Here, we tackle this challenge using
strain-tunable GaAs quantum dots driven under two-photon resonant excitation
and with strictly-degenerate exciton states. We demonstrate experimentally that
our on-demand source generates polarization-entangled photons with fidelity of
0.978(5) and concurrence of 0.97(1) without resorting to post-selection
techniques. Moreover, we show that the remaining decoherence mechanisms can be
overcome using a modest Purcell enhancement so as to achieve a degree of
entanglement >0.99. Our results highlight that GaAs quantum dots can be readily
used in advanced communication protocols relying on the non-local properties of
quantum entanglement
Highly indistinguishable single photons from incoherently and coherently excited GaAs quantum dots
Semiconductor quantum dots are converging towards the demanding requirements
of photonic quantum technologies. Among different systems, quantum dots with
dimensions exceeding the free-exciton Bohr radius are appealing because of
their high oscillator strengths. While this property has received much
attention in the context of cavity quantum electrodynamics, little is known
about the degree of indistinguishability of single photons consecutively
emitted by such dots and on the proper excitation schemes to achieve high
indistinguishability. A prominent example is represented by GaAs quantum dots
obtained by local droplet etching, which recently outperformed other systems as
triggered sources of entangled photon pairs. On these dots, we compare
different single-photon excitation mechanisms, and we find (i) a "phonon
bottleneck" and poor indistinguishability for conventional excitation via
excited states and (ii) photon indistinguishablilities above 90% for both
strictly resonant and for incoherent acoustic- and optical-phonon-assisted
excitation. Among the excitation schemes, optical phonon-assisted excitation
enables straightforward laser rejection without a compromise on the source
brightness together with a high photon indistinguishability
Populist citizens in four European countries: Widespread dissatisfaction goes with contradictory but pro-democratic regime preferences
Are populist citizens a threat to democracy? Some philosophers view populism and democracy as irreconcilable conceptions of governing. Another line of thought describes populism as useful democratic corrective. Drawing on nationally representative surveys from four European countries, this study investigates how European populist citizens think about democracy. Descriptive analyses reveal that populist worldviews only weakly predict how people think about democracy. On average, populist and non-populist citizens aspire to similar kinds of political systems and both endorse liberal-democratic institutions. Yet, populists and non-populists differ in the degree to which they hold inconsistent beliefs. Citizens with populist outlook more frequently express contradictory demands that political institutions cannot possibly deliver. Based on these findings, we conclude that most populist citizens do not pursue an elaborate anti-democratic conception of governing. Rather, the widespread dissatisfaction among populists may create an indeterminate openness for institutional change that political elites could steer in different directions
Neither a trait nor wildly fluctuating: On the stability of populist attitudes and its implications for empirical research
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