129 research outputs found
Coherent Time Evolution and Boundary Conditions of Two-Photon Quantum Walks
Multi-photon quantum walks in integrated optics are an attractive controlled
quantum system, that can mimic less readily accessible quantum systems and
exhibit behavior that cannot in general be accurately replicated by classical
light without an exponential overhead in resources. The ability to observe time
evolution of such systems is important for characterising multi-particle
quantum dynamics---notably this includes the effects of boundary conditions for
walks in spaces of finite size. Here we demonstrate the coherent evolution of
quantum walks of two indistinguishable photons using planar arrays of 21
evanescently coupled waveguides fabricated in silicon oxynitride technology. We
compare three time evolutions, that follow closely a model assuming unitary
evolution, corresponding to three different lengths of the array---in each case
we observe quantum interference features that violate classical predictions.
The longest array includes reflecting boundary conditions.Comment: 7 pages,7 figure
Quantum walks of correlated photon pairs in two-dimensional waveguide arrays
We demonstrate quantum walks of correlated photons in a 2D network of
directly laser written waveguides coupled in a 'swiss cross' arrangement. The
correlated detection events show high-visibility quantum interference and
unique composite behaviour: strong correlation and independence of the quantum
walkers, between and within the planes of the cross. Violations of a
classically defined inequality, for photons injected in the same plane and in
orthogonal planes, reveal non-classical behaviour in a non-planar structure.Comment: 5 pages, 5 figure
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Reengineering of interbank networks
We investigate the reengineeering of interbank networks with a specific focus on capital increase. We consider a scenario where all other components of the network’s infrastructure remain stable (a practical assumption for short-term situations). Our objective is to assess the impact of raising capital on the network’s robustness and to address the following key aspects. First, given a predefined target for network robustness, our aim is to achieve this goal optimally, minimizing the required capital increase. Second, in cases where a total capital increase has been determined, the central challenge lies in distributing this increase among the banks in a manner that maximizes the stability of the network. To tackle these challenges, we begin by developing a comprehensive theoretical framework. Subsequently, we formulate an optimization model for the network’s redesign. Finally, we apply this framework to practical examples, highlighting its applicability in real-world scenarios
Photonic Quantum Logic with Narrowband Light from Single Atoms
Increasing control of single photons enables new applications of photonic
quantum-enhanced technology and further experimental exploration of fundamental
quantum phenomena. Here, we demonstrate quantum logic using narrow linewidth
photons that are produced under nearly perfect quantum control from a single
^87Rb atom strongly coupled to a high-finesse cavity. We use a controlled- NOT
gate integrated into a photonic chip to entangle these photons, and we observe
non-classical correlations between events separated by periods exceeding the
travel time across the chip by three orders of magnitude. This enables quantum
technology that will use the properties of both narrowband single photon
sources and integrated quantum photonics, such as networked quantum computing,
narrow linewidth quantum enhanced sensing and atomic memories.Comment: 5 pates, 3 figure
The nonrelativistic limit of the Majorana equation and its simulation in trapped ions
We analyze the Majorana equation in the limit where the particle is at rest.
We show that several counterintuitive features, absent in the rest limit of the
Dirac equation, do appear. Among them, Dirac-like positive energy solutions
that turn into negative energy ones by free evolution, or nonstandard
oscillations and interference between real and imaginary spinor components for
complex solutions. We also study the ultrarelativistic limit, showing that the
Majorana and Dirac equations mutually converge. Furthermore, we propose a
physical implementation in trapped ions.Comment: 7 pages, 1 figure. Proceedings of 18th Central European Workshop on
Quantum Optics (CEWQO 2011), Madrid, Spai
Quantum walks of correlated particles
Quantum walks of correlated particles offer the possibility to study
large-scale quantum interference, simulate biological, chemical and physical
systems, and a route to universal quantum computation. Here we demonstrate
quantum walks of two identical photons in an array of 21 continuously
evanescently-coupled waveguides in a SiOxNy chip. We observe quantum
correlations, violating a classical limit by 76 standard deviations, and find
that they depend critically on the input state of the quantum walk. These
results open the way to a powerful approach to quantum walks using correlated
particles to encode information in an exponentially larger state space
High-quality polarization entanglement state preparation and manipulation in standard telecommunication channels
We report a novel and simple approach for generating near-perfect quality
polarization entanglement in a fully guided-wave fashion. Both deterministic
pair separation into two adjacent telecommunication channels and the paired
photons' temporal walk-off compensation are achieved using standard fiber
components. Two-photon interference experiments are performed, both for
quantitatively demonstrating the relevance of our approach, and for
manipulating the produced state between bosonic and fermionic symmetries. The
compactness, versatility, and reliability of this configuration makes it a
potential candidate for quantum communication applications.Comment: 6 figure
Microwave spectroscopy of radio-frequency-dressed 87Rb
We study the hyper fine spectrum of atoms of 87Rb dressed by a radio-frequency field and present experimental results in three different situations: freely falling atoms, atoms trapped in an optical dipole trap, and atoms in an adiabatic radio-frequency dressed shell trap. In all cases, we observe several resonant sidebands spaced (in frequency) at intervals equal to the dressing frequency, corresponding to transitions enabled by the dressing field. We theoretically explain the main features of the microwave spectrum using a semiclassical model in the low-field limit and the rotating-wave approximation for alkali-metal-like species, in general, and 87Rb atoms, in particular. As a proof of concept, we demonstrate how the spectral signal of a dressed atomic ensemble enables an accurate determination of the dressing configuration and the probing microwave field
Morphometric Relationship, Phylogenetic Correlation, and Character Evolution in the Species-Rich Genus Aphis (Hemiptera: Aphididae)
The species-rich genus Aphis consists of more than 500 species, many of them host-specific on a wide range of plants, yet very similar in general appearance due to convergence toward particular morphological types. Most species have been historically clustered into four main phenotypic groups (gossypii, craccivora, fabae, and spiraecola groups). To confirm the morphological hypotheses between these groups and to examine the characteristics that determine them, multivariate morphometric analyses were performed using 28 characters measured/counted from 40 species. To infer whether the morphological relationships are correlated with the genetic relationships, we compared the morphometric dataset with a phylogeny reconstructed from the combined dataset of three mtDNA and one nuclear DNA regions.Based on a comparison of morphological and molecular datasets, we confirmed morphological reduction or regression in the gossypii group unlike in related groups. Most morphological characteristics of the gossypii group were less variable than for the other groups. Due to these, the gossypii group could be morphologically well separated from the craccivora, fabae, and spiraecola groups. In addition, the correlation of the rates of evolution between morphological and DNA datasets was highly significant in their diversification.The morphological separation between the gossypii group and the other species-groups are congruent with their phylogenetic relationships. Analysis of trait evolution revealed that the morphological traits found to be significant based on the morphometric analyses were confidently correlated with the phylogeny. The dominant patterns of trait evolution resulting in increased rates of short branches and temporally later evolution are likely suitable for the modality of Aphis speciation because they have adapted species-specifically, rapidly, and more recently on many different host plants
Hypertonic Stress Induces VEGF Production in Human Colon Cancer Cell Line Caco-2: Inhibitory Role of Autocrine PGE2
Vascular Endothelial Growth Factor (VEGF) is a major regulator of angiogenesis. VEGF expression is up regulated in response to micro-environmental cues related to poor blood supply such as hypoxia. However, regulation of VEGF expression in cancer cells is not limited to the stress response due to increased volume of the tumor mass. Lipid mediators in particular arachidonic acid-derived prostaglandin (PG)E2 are regulators of VEGF expression and angiogenesis in colon cancer. In addition, increased osmolarity that is generated during colonic water absorption and feces consolidation seems to activate colon cancer cells and promote PGE2 generation. Such physiological stimulation may provide signaling for cancer promotion. Here we investigated the effect of exposure to a hypertonic medium, to emulate colonic environment, on VEGF production by colon cancer cells. The role of concomitant PGE2 generation and MAPK activation was addressed by specific pharmacological inhibition. Human colon cancer cell line Caco-2 exposed to a hypertonic environment responded with marked VEGF and PGE2 production. VEGF production was inhibited by selective inhibitors of ERK 1/2 and p38 MAPK pathways. To address the regulatory role of PGE2 on VEGF production, Caco-2 cells were treated with cPLA2 (ATK) and COX-2 (NS-398) inhibitors, that completely block PGE2 generation. The Caco-2 cells were also treated with a non selective PGE2 receptor antagonist. Each treatment significantly increased the hypertonic stress-induced VEGF production. Moreover, addition of PGE2 or selective EP2 receptor agonist to activated Caco-2 cells inhibited VEGF production. The autocrine inhibitory role for PGE2 appears to be selective to hypertonic environment since VEGF production induced by exposure to CoCl2 was decreased by inhibition of concomitant PGE2 generation. Our results indicated that hypertonicity stimulates VEGF production in colon cancer cell lines. Also PGE2 plays an inhibitory role on VEGF production by Caco-2 cells exposed to hyperosmotic stress through EP2 activation
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