4,142 research outputs found

    Generation Engineering of Heralded Narrowband Colour Entangled States

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    Efficient heralded generation of entanglement together with its manipulation is of great importance for quantum communications. In addition, states generated with bandwidths naturally compatible with atomic transitions allow a more efficient mapping of light into matter which is an essential requirement for long distance quantum communications. Here we propose a scheme where the indistinguishability between two spontaneous four-wave mixing processes is engineered to herald generation of single-photon frequency-bin entangled states, i.e., single-photons shared by two distinct frequency modes. We show that entanglement can be optimised together with the generation probability, while maintaining absorption negligible. Besides, the scheme illustrated for cold rubidium atoms is versatile and can be implemented in several other physical systems

    Radiation 'damping' in atomic photonic crystals

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    The force exerted on a material by an incident beam of light is dependent upon the material's velocity in the laboratory frame of reference. This velocity dependence is known to be diffcult to measure, as it is proportional to the incident optical power multiplied by the ratio of the material velocity to the speed of light. Here we show that this typically tiny effect is greatly amplified in multilayer systems composed of resonantly absorbing atoms (e.g. optically trapped 87Rb), which may exhibit ultra-narrow photonic band gaps. The amplification of the effect is shown to be three orders of magnitude greater than previous estimates for conventional photonic-band-gap materials, and significant for material velocities of a few ms/s.Comment: 5 pages, 3 figure

    Optically Tunable Photonic Stop Bands in Homogeneous Absorbing Media.

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    Resonantly absorbing media supporting electromagnetically induced transparency may give rise to specific periodic patterns where a light probe is found to experience a fully developed photonic band gap yet with negligible absorption everywhere. In ultracold atomic samples the gap is found to arise from spatial regions where Autler-Townes splitting and electromagnetically induced transparency alternate with one another and detailed calculations show that accurate and efficient coherent optical control of the gap can be accomplished. The remarkable experimental simplicity of the control scheme would ease quantum nonlinear optics applications

    Photons on a leash

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    Quantum coherence and interference can be used to control the light-matter interaction and the propagation of light in multilevel systems. Effects of electromagnetically induced transparency based on exciton and biexciton levels or on impurity levels in solid-state media are here reviewed. New photonic crystal structures created via coherent optical nonlinearities in such solid media are also considered and discusse

    Perinatal stem cells revisited: directions and indications at the crossroads between tissue regeneration and repair.

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    Perinatal stem cells research attracted great interest worldwide in recent years. Foetus-associated tissues contain various populations of stem cells, most of which are comprised within the category of mesenchymal stem cells (MSCs). This special issue collects both reviews and original reports on all the perinatal stem cell types which are currently under investigation. These cells have multiple promising features: differentiative capacity towards mature cell types of all the three germ layers, hypoimmunogenicity in vitro and in vivo, ease of sourcing, ex vivo culture and stor- age. In particular, immune modulation is viewed as a prom- ising feature of many MSCs populations, since these cells, once administered therapeutically, may be able to overcome, or at least evade, the host immune response which may lead to acute or chronic rejection of the transplant

    #Covid-19: A hashtag for examining reactions towards Europe in times of crisis. An analysis of tweets in Italian, Spanish, and French

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    Hashtag research has established itself as a relevant research field, with various studies having analysed this polysemic collector in crisis and media events. Hashtags are used in social media, most specifically on Twitter. Further, between 2020 and 2021, hashtag studies linked to the COVID-19 pandemic have emerged. Accordingly, this study aimed to analyse the content of tweets during the first phase of the COVID-19 pandemic (March 4-11, 2020) that included the hashtag #Covid-19 in three different languages: Italian, Spanish, and French. For these analyses, we used emotional text mining. The goal of this study was to reconstruct the representation of the pandemic, of containment measures, and of Europe in tweets. We discussed the prevailing attitude towards Europe in times of crisis

    Roles of the Core Components of the Mammalian miRISC in Chromatin Biology

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    The Argonaute (AGO) and the Trinucleotide Repeat Containing 6 (TNRC6) family proteins are the core components of the mammalian microRNA-induced silencing complex (miRISC), the machinery that mediates microRNA function in the cytoplasm. The cytoplasmic miRISC-mediated post-transcriptional gene repression has been established as the canonical mechanism through which AGO and TNRC6 proteins operate. However, growing evidence points towards an additional mechanism through which AGO and TNRC6 regulate gene expression in the nucleus. While several mechanisms through which miRISC components function in the nucleus have been described, in this review we aim to summarize the major findings that have shed light on the role of AGO and TNRC6 in mammalian chromatin biology and on the implications these novel mechanisms may have in our understanding of regulating gene expression
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