An entangled-light-emitting diode Farrer, I; Ritchie, D. A; Shields, A. J ...
Nature,
06/2010, Letnik:
465, Številka:
7298
Journal Article
Recenzirano
An optical quantum computer, powerful enough to solve problems so far intractable using conventional digital logic, requires a large number of entangled photons. At present, entangled-light sources ...are optically driven with lasers, which are impractical for quantum computing owing to the bulk and complexity of the optics required for large-scale applications. Parametric down-conversion is the most widely used source of entangled light, and has been used to implement non-destructive quantum logic gates. However, these sources are Poissonian and probabilistically emit zero or multiple entangled photon pairs in most cycles, fundamentally limiting the success probability of quantum computational operations. These complications can be overcome by using an electrically driven on-demand source of entangled photon pairs, but so far such a source has not been produced. Here we report the realization of an electrically driven source of entangled photon pairs, consisting of a quantum dot embedded in a semiconductor light-emitting diode (LED) structure. We show that the device emits entangled photon pairs under d.c. and a.c. injection, the latter achieving an entanglement fidelity of up to 0.82. Entangled light with such high fidelity is sufficient for application in quantum relays, in core components of quantum computing such as teleportation, and in entanglement swapping. The a.c. operation of the entangled-light-emitting diode (ELED) indicates its potential function as an on-demand source without the need for a complicated laser driving system; consequently, the ELED is at present the best source on which to base future scalable quantum information applications.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Abstract
The All-Sky Automated Survey for Supernovae (ASAS-SN) is the first optical survey to routinely monitor the whole sky with a cadence of ∼2–3 d down to V ≲ 17 mag. ASAS-SN has monitored the ...whole sky since 2014, collecting ∼100–500 epochs of observations per field. The V-band light curves for candidate variables identified during the search for supernovae are classified using a random forest classifier and visually verified. We present a catalogue of 66 179 bright, new variable stars discovered during our search for supernovae, including 27 479 periodic variables and 38 700 irregular variables. V-band light curves for the ASAS-SN variables are available through the ASAS-SN variable stars data base
(https://asas-sn.osu.edu/variables). The data base will begin to include the light curves of known variable stars in the near future along with the results for a systematic, all-sky variability survey.
ABSTRACT
The All-Sky Automated Survey for Supernovae (ASAS-SN) provides long baseline (∼4 yr) light curves for sources brighter than V ≲ 17 mag across the whole sky. As part of our effort to ...characterize the variability of all the stellar sources visible in ASAS-SN, we have produced ∼30.1 million V-band light curves for sources in the Southern hemisphere using the APASS DR9 (AAVSO Photometric All-Sky Survey Data Release) catalogue as our input source list. We have systematically searched these sources for variability using a pipeline based on random forest classifiers. We have identified ${\sim } 220\, 000$ variables, including ${\sim } 88\, 300$ new discoveries. In particular, we have discovered ${\sim }48\, 000$ red pulsating variables, ${\sim }23\, 000$ eclipsing binaries, ∼2200 δ-Scuti variables, and ${\sim }10\, 200$ rotational variables. The light curves and characteristics of the variables are all available through the ASAS-SN variable stars data base (https://asas-sn.osu.edu/variables). The pre-computed ASAS-SN V-band light curves for all the ∼30.1 million sources are available through the ASAS-SN photometry data base (https://asas-sn.osu.edu/photometry). This effort will be extended to provide ASAS-SN light curves for sources in the Northern hemisphere and for V ≲ 17 mag sources across the whole sky that are not included in APASS DR9.
Dental care professionals (DCPs) are thought to be at enhanced risk of occupational exposure to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). However, robust data to support this from ...large-scale seroepidemiological studies are lacking. We report a longitudinal seroprevalence analysis of antibodies to SARS-CoV-2 spike glycoprotein, with baseline sampling prior to large-scale practice reopening in July 2020 and follow-up postimplementation of new public health guidance on infection prevention control (IPC) and enhanced personal protective equipment (PPE). In total, 1,507 West Midlands DCPs were recruited into this study in June 2020. Baseline seroprevalence was determined using a combined IgGAM enzyme-linked immunosorbent assay and the cohort followed longitudinally for 6 mo until January/February 2021 through the second wave of the coronavirus disease 2019 pandemic in the United Kingdom and vaccination commencement. Baseline seroprevalence was 16.3%, compared to estimates in the regional population of 6% to 7%. Seropositivity was retained in over 70% of participants at 3- and 6-mo follow-up and conferred a 75% reduced risk of infection. Nonwhite ethnicity and living in areas of greater deprivation were associated with increased baseline seroprevalence. During follow-up, no polymerase chain reaction–proven infections occurred in individuals with a baseline anti–SARS-CoV-2 IgG level greater than 147.6 IU/ml with respect to the World Health Organization international standard 20-136. After vaccination, antibody responses were more rapid and of higher magnitude in those individuals who were seropositive at baseline. Natural infection with SARS-CoV-2 prior to enhanced PPE was significantly higher in DCPs than the regional population. Natural infection leads to a serological response that remains detectable in over 70% of individuals 6 mo after initial sampling and 9 mo from the peak of the first wave of the pandemic. This response is associated with protection from future infection. Even if serological responses wane, a single dose of the Pfizer-BioNTech 162b vaccine is associated with an antibody response indicative of immunological memory.
Atmospheric rivers (ARs) constitute an important mechanism for water vapor transport, but research on their characteristics and impacts has relied on a diverse assortment of detection methodologies, ...complicating comparisons. The AR Tracking Method Intercomparison Project (ARTMIP) provides a platform for comparing such methodologies, but analysis of ARTMIP catalogues has heretofore focused primarily on specific regions. Here we investigate ARs as detected by an ensemble of algorithms with global coverage. We find that the frequency of occurrence of the majority‐consensus ARs produces a robust distribution, featuring five hot spots over the extratropical oceans, against which we compare individual algorithm results. We further explore the underlying similarities and differences via two case studies of AR evolution. The dominant source of disagreement between detection methodologies globally consists of detections (or lack thereof) of weak features, and the algorithms otherwise tend to agree remarkably well on the footprints of ARs.
Plain Language Summary
Atmospheric rivers—filamentary structures in the atmosphere in which water vapor is concentrated and transported—have received increasing attention over the past decade, but studies of their occurrence have relied on many disparate methods for objectively detecting them in various data sets. Here we explore the results of fourteen different such methods applied to the same data set, to better understand the resulting consensus or disagreement on atmospheric river occurrence, using both statistics from 37 years and two specific case studies. We find that most methods tend to agree quantitatively when detecting moderate and stronger features (in which the water vapor transport is high), and what appears to be significant disagreement is simply due to regions of only slightly enhanced vapor transport that are obviously disputable as true atmospheric rivers.
Key Points
Agreement on global atmospheric river detections is investigated using global catalogues from Atmospheric River Tracking Method Intercomparison Project
Ensemble majority consensus on ARs provides more robust occurrence frequencies than ensemble average frequencies
Algorithms tend to agree quantitatively on moderate atmospheric rivers, and most discrepancy is explained by detection of marginal small or weak features
The Atmospheric River Tracking Method Intercomparison Project
(ARTMIP) is an international collaborative effort to understand and quantify
the uncertainties in atmospheric river (AR) science based on ...detection
algorithm alone. Currently, there are many AR identification and tracking
algorithms in the literature with a wide range of techniques and conclusions.
ARTMIP strives to provide the community with information on different
methodologies and provide guidance on the most appropriate algorithm for a
given science question or region of interest. All ARTMIP participants will
implement their detection algorithms on a specified common dataset for a
defined period of time. The project is divided into two phases: Tier 1 will
utilize the Modern-Era Retrospective analysis for Research and Applications,
version 2 (MERRA-2) reanalysis from January 1980 to June 2017 and will be
used as a baseline for all subsequent comparisons. Participation in Tier 1 is
required. Tier 2 will be optional and include sensitivity studies designed
around specific science questions, such as reanalysis uncertainty and climate
change. High-resolution reanalysis and/or model output will be used wherever
possible. Proposed metrics include AR frequency, duration, intensity, and
precipitation attributable to ARs. Here, we present the ARTMIP experimental
design, timeline, project requirements, and a brief description of the
variety of methodologies in the current literature. We also present results
from our 1-month “proof-of-concept” trial run designed to illustrate the
utility and feasibility of the ARTMIP project.
The signature of coherent coupling between two quantum states is an anticrossing in their energies as one is swept through the other. In single semiconductor quantum dots containing an electron-hole ...pair the eigenstates form a two-level system that can be used to demonstrate quantum effects in the solid state, but in all previous work these states were independent. Here we describe a technique to control the energetic splitting of these states using a vertical electric field, facilitating the observation of coherent coupling between them. Near the minimum splitting the eigenstates rotate in the plane of the sample, being orientated at 45° when the splitting is smallest. Using this system we show direct control over the exciton states in one quantum dot, leading to the generation of entangled photon pairs.
Quantum networks can interconnect remote quantum information processors, allowing interaction between different architectures and increasing net computational power. Fibre-optic telecommunications ...technology offers a practical platform for routing weakly interacting photonic qubits, allowing quantum correlations and entanglement to be established between distant nodes. Although entangled photons have been produced at telecommunications wavelengths using spontaneous parametric downconversion in nonlinear media, as system complexity increases their inherent excess photon generation will become limiting. Here we demonstrate entangled photon pair generation from a semiconductor quantum dot at a telecommunications wavelength. Emitted photons are intrinsically anti-bunched and violate Bell's inequality by 17 standard deviations High-visibility oscillations of the biphoton polarization reveal the time evolution of the emitted state with exceptional clarity, exposing long coherence times. Furthermore, we introduce a method to evaluate the fidelity to a time-evolving Bell state, revealing entanglement between photons emitted up to 5 ns apart, exceeding the exciton lifetime.
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