Search for: All records

Abstract Secret-key distillation from quantum states and channels is a central task of interest in quantum information theory, as it facilitates private communication over a quantum network. Here, we study the task of secret-key distillation from bipartite states and point-to-point quantum channels using local operations and one-way classical communication (one-way LOCC). We employ the resource theory of unextendible entanglement to study the transformation of a bipartite state under one-way LOCC, and we obtain several efficiently computable upper bounds on the number of secret bits that can be distilled from a bipartite state using one-way LOCC channels; these findings apply not only in the one-shot setting but also in some restricted asymptotic settings. We extend our formalism to private communication over a quantum channel assisted by forward classical communication. We obtain efficiently computable upper bounds on the one-shot forward-assisted private capacity of a channel, thus addressing a question in the theory of quantum-secured communication that has been open for some time now. Our formalism also provides upper bounds on the rate of private communication when using a large number of channels in such a way that the error in the transmitted private data decreases exponentially with the number of channel uses. Moreover, our bounds can be computed using semidefinite programs, thus providing a computationally feasible method to understand the limits of private communication over a quantum network. 

In northern India and surrounding countries of the Lower Himalaya, apple is an important cash crop that contributes significantly to state economies and farmer livelihoods. Apple cultivation is shifting to higher elevations to counter declining fruit yields associated with climate change. Pollinator scarcity is another factor linked to declines in fruit yield and quality. To advance understanding of bee diversity and pollination ecology in apples for this region, we compiled a taxonomically updated list of bee taxa associated with apple orchards using records from existing literature and a new field study. Our list includes 25 bee genera, 75 named species, and numerous morphospecies. Common genera also feature prominently in apple studies elsewhere in the world. Apis cerana and A. mellifera were the most frequently reported visitors to apple flowers; Bombus, Ceratina, Lasioglossum, and Syrphidae flies were the most common non-Apis floral visitors. Bee species richness was inversely correlated with elevation and pollination deficit whereas bee abundance was not. Therefore, apples grown at higher elevations may experience more favourable growing conditions but also incur greater pollination deficits that are linked to reduced bee richness. This underscores the importance of conserving bee diversity to safeguard pollination services and farmer livelihoods in the region. Our literature review further highlights the need for more tools to identify the regional bee fauna, more thoroughly documented and standardised study methods to build capacity within the research community and aid comparative studies, and more expansive cataloguing and monitoring of pollinator communities to better understand the diversity, roles, and status of bees throughout this under-studied region.