Quantum optical communication in the presence of strong attenuation noise

Is quantum communication possible over an optical fiber with transmissivity less or equal to one half? The answer is well known to be negative if the environment with which the incoming signal interacts is initialized in a thermal state. However, Lami et al. [Phys. Rev. Lett. 125, 110504 (2020)] found the quantum capacity to be always bounded away from zero for all positive values of the transmissivity, a phenomenon dubbed “die-hard quantum communication” (D-HQCOM), provided that the initial environment state can be chosen appropriately, depending on the transmissivity. Here we show an even stronger version of D-HQCOM in the context of entanglement-assisted classical communication: entanglement assistance and control of the environment enable communication with performance at least equal to that of the ideal case of absence of noise, even if the transmissivity is arbitrarily small (but strictly positive). These two phenomena of D-HQCOM have technological potential provided that we are able to control the environment. How can we achieve this? Our second main result answers this question. Here we provide a fully consistent protocol to activate the phenomena of D-HQCOM without directly accessing the environment state. This is done by sending over the channel “trigger signals,” i.e., signals which do not encode information, prior to the actual communication, with the goal of modifying the environment in an advantageous way. This is possible due to the memory effects which arise when the sender feeds signals separated by a sufficiently short temporal interval. Our results may offer a concrete scheme to communicate across arbitrarily long optical fibers, without using quantum repeaters. As a by-product of our analysis, we derive a simple Kraus representation of the thermal attenuator exploiting the associated Lindblad master equation

Restoring Quantum Communication Efficiency over High Loss Optical Fibers

In the absence of quantum repeaters, quantum communication proved to be nearly impossible across optical fibers longer than greater than or similar to 20 km due to the drop of transmissivity below the critical threshold of 1/2. However, if the signals fed into the fiber are separated by a sufficiently short time interval, memory effects must be taken into account. In this Letter, we show that by properly accounting for these effects it is possible to devise schemes that enable unassisted quantum communication across arbitrarily long optical fibers at a fixed positive qubit transmission rate. We also demonstrate how to achieve entanglement-assisted communication over arbitrarily long distances at a rate of the same order of the maximum achievable in the unassisted noiseless case

Maximum tolerable excess noise in CV-QKD and improved lower bound on two-way capacities

The two-way capacities of quantum channels determine the ultimate entanglement distribution rates achievable by two distant parties that are connected by a noisy transmission line, in absence of quantum repeaters. Since repeaters will likely be expensive to build and maintain, a central open problem of quantum communication is to understand what performances are achievable without them. In this paper, we find a new lower bound on the energy-constrained and unconstrained two-way quantum and secret-key capacities of all phase-insensitive bosonic Gaussian channels, namely thermal attenuator, thermal amplifier, and additive Gaussian noise, which are realistic models for the noise affecting optical fibres or free-space links. Ours is the first nonzero lower bound in the parameter range where the (reverse) coherent information becomes negative, and it shows explicitly that entanglement distribution is always possible when the channel is not entanglement breaking. In addition, our construction is fully explicit, i.e. we devise and optimise a concrete entanglement distribution and distillation protocol that works by combining recurrence and hashing protocols.Comment: 41 pages, 11 figure

Learning sustainability by making games. The experience of a challenge as a novel approach for Education for Sustainable Development

[EN] Nowadays, the programs of Education for Sustainable Development (ESD) are designed for changing attitudes on environmental, economic, and social dimensions. In this context, and considering the varied ages of the participating students, it is necessary to implement appropriate pedagogical methods that are generally different from the traditional ones. Among the available approaches, Sustainability serious games (SSGs) appear to be an ideal candidate to facilitate ESD providing students with opportunities to experience the complex issues of sustainability. Besides learning by playing SSG, another relevant opportunity, capable of engaging teachers and students into a relevant and meaningful learning context, is learning by making SSGs, capable of engaging teachers and students into a relevant and meaningful learning context. In light of these comments, this paper proposes a major contribution to the research on learning by making games through a detailed discussion of the results obtained during a University Challenge experience, where students were involved in the design and development of SSGs. The Challenge involved 59 higher education (HE) students who were asked to work in groups to create a (per-group) prototype of a SSG aimed at improving the sustainability of our campus. Results of the Challenge assessment show that this learning approach can indeed be considered a valuable alternative for ESD.Cravero, S.; Strada, F.; Lami, I.; Bottino, A. (2021). Learning sustainability by making games. The experience of a challenge as a novel approach for Education for Sustainable Development. En 7th International Conference on Higher Education Advances (HEAd'21). Editorial Universitat Politècnica de València. 651-659. https://doi.org/10.4995/HEAd21.2021.13192OCS65165

Ground-dwelling arthropods as biodiversity indicators in maize agroecosystems of Northern Italy

Reliable monitoring of arthropod diversity in a given agroecosystem is essential for the conservation of the related ecosystem services, such as biological control. The often daunting complexity of arthropod collection and identification, however, highlights the need for surrogate taxa that can be easily sampled and be representative of a number of other taxa in term of diversity, general community features and specific composition. In this study, we used pitfall traps to sample three ground-dwelling arthropod taxa important as biocontrol agents (ground beetles, rove beetles and spiders) in 9 conventionally managed maize agroecosystems of Northern Italy over the course of two years, with the goal of characterizing their assemblages and evaluating their reciprocal potential as indicators of activity density, species richness, community turnover and species co-occurrence. Although dominated by few generalist species, sampled arthropod communities were relatively species-rich, and included the first Italian record of the spider Zelotes metellus (Roewer) (Araneae: Gnaphosidae). Ground beetles as a group were confirmed as promising indicators for the species richness and community composition turnover of rove beetles and spiders. Additionally, several abundant arthropod species acted as indicators of the species richness of their respective groups, and the ground beetle Pterostichus macer (Marsham) also worked as an indicator of overall rove beetle activity density. While the co-occurrence of individual arthropod species was limited for the studied taxa, a few species such as the ground beetle Parophonus maculicornis (Duftschmid) did show promise as species-specific bioindicators. Our results could be useful in improving the monitoring and management of these important natural enemies in maize-growing regions

coastal erosion triggered by political and socio economical abrupt changes the case of lalzit bay albania

Countries that undergo abrupt changes in their political regimes, such as the transition from totalitarianism to systems based on democratic principles, experience socio-economic changes that may also have a direct impact on the trans- formation and the anthropic pressure applied to the environment. This can ranges from the scale of small communities to larger spatial scales, such as that of a catchment basin. The rise of a liberal society in countries such as the Eastern European nations, often lacks a structure capable of regulating and planning the development of the territory and the use of natural resources, which should be aimed at conciliating the new development needs with the sustainable man- agement of the environment. This paper describes and analyses the extensive coastal erosion that has taken place over the past thirty years in Lalzit Bay, Albania, which may be attributed to the great social and economic transformations that occurred in the country after the fall of Enver Hoxa's communist regime in 1991, and the consequent changes in land use. These led to a significant reduction in the volume of sediment carried by rivers, which was necessary for the morphological equilibrium of the coast and its natural replenishment

Pseudoscalar decay constants fK/fπf_K/f_\pi, fDf_D and fDsf_{D_s} with Nf=2+1+1N_f = 2 + 1 + 1 ETMC congurations

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Factors determining variation in colour morph frequencies in invasive Harmonia axyridis populations

The Harlequin ladybird Harmonia axyridis Pallas, native to eastern Asia, is an invasive, non-native species that has recently achieved an almost worldwide distribution. A conspicuous feature of this species is colour polymorphism of the elytra. In its native area, the populations consist of a recessive non-melanic morph, several dominant melanic morphs and small numbers of other (rare) morphs. The morph proportions in native populations have been intensively studied and vary with geographic area, climate and time. In contrast, colour polymorphism in invaded regions has been little studied. We examine and try to account for the morph frequencies observed across the different invaded regions. In America, monomorphic populations consist of the non-melanic morphs while European populations contain also melanic morphs. In particular geographic areas of Europe, the average percentage of the non-melanic morphs varied between 78 and 99%. It was highest in the lowlands of northern Italy and central and northern Europe and decreased in the Alps and western (Spain, UK) and eastern (southeast Russia) margins of the recently invaded area. In central Europe the frequency of the non-melanic morphs decreased over the course of the year but increased over the years from 2010 to 2018. The local differences might thus arise through gradual change of the morph composition of the founder invasive, non-native population. However, the variation in non-melanic morph frequency was not correlated with climatic characteristics that might affect coccinellid polymorphism. The observed rate of change in morph proportions in our data was too small to explain the diversification of what was supposedly a uniform invasive, non-native population at the point of introduction

Mapping 123 million neonatal, infant and child deaths between 2000 and 2017

Since 2000, many countries have achieved considerable success in improving child survival, but localized progress remains unclear. To inform efforts towards United Nations Sustainable Development Goal 3.2—to end preventable child deaths by 2030—we need consistently estimated data at the subnational level regarding child mortality rates and trends. Here we quantified, for the period 2000–2017, the subnational variation in mortality rates and number of deaths of neonates, infants and children under 5 years of age within 99 low- and middle-income countries using a geostatistical survival model. We estimated that 32% of children under 5 in these countries lived in districts that had attained rates of 25 or fewer child deaths per 1,000 live births by 2017, and that 58% of child deaths between 2000 and 2017 in these countries could have been averted in the absence of geographical inequality. This study enables the identification of high-mortality clusters, patterns of progress and geographical inequalities to inform appropriate investments and implementations that will help to improve the health of all populations

Mapping child growth failure across low- and middle-income countries

Child growth failure (CGF), manifested as stunting, wasting, and underweight, is associated with high 5 mortality and increased risks of cognitive, physical, and metabolic impairments. Children in low- and middle-income countries (LMICs) face the highest levels of CGF globally. Here we illustrate national and subnational variation of under-5 CGF indicators across LMICs, providing 2000–2017 annual estimates mapped at a high spatial resolution and aggregated to policy-relevant administrative units and national levels. Despite remarkable declines over the study period, many LMICs remain far from the World Health 10 Organization’s ambitious Global Nutrition Targets to reduce stunting by 40% and wasting to less than 5% by 2025. Large disparities in prevalence and rates of progress exist across regions, countries, and within countries; our maps identify areas where high prevalence persists even within nations otherwise succeeding in reducing overall CGF prevalence. By highlighting where subnational disparities exist and the highest-need populations reside, these geospatial estimates can support policy-makers in planning locally 15 tailored interventions and efficient directing of resources to accelerate progress in reducing CGF and its health implications