4,318 research outputs found

    Fast optimization of parametrized quantum optical circuits

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    Parametrized quantum optical circuits are a class of quantum circuits in which the carriers of quantum information are photons and the gates are optical transformations. Classically optimizing these circuits is challenging due to the infinite dimensionality of the photon number vector space that is associated to each optical mode. Truncating the space dimension is unavoidable, and it can lead to incorrect results if the gates populate photon number states beyond the cutoff. To tackle this issue, we present an algorithm that is orders of magnitude faster than the current state of the art, to recursively compute the exact matrix elements of Gaussian operators and their gradient with respect to a parametrization. These operators, when augmented with a non-Gaussian transformation such as the Kerr gate, achieve universal quantum computation. Our approach brings two advantages: first, by computing the matrix elements of Gaussian operators directly, we don't need to construct them by combining several other operators; second, we can use any variant of the gradient descent algorithm by plugging our gradients into an automatic differentiation framework such as TensorFlow or PyTorch. Our results will find applications in quantum optical hardware research, quantum machine learning, optical data processing, device discovery and device design.Comment: 21 pages, 10 figure

    Broadband pseudothermal states with tunable spectral coherence generated via nonlinear optics

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    It is well known that the reduced state of a two-mode squeezed vacuum state is a thermal state---i.e. a state whose photon-number statistics obey a geometric distribution. More exotic \emph{broadband} states can be realized as the reduced state of two spectrally-entangled beams generated using nonlinear optics. We show that these broadband "pseudothermal" states are tensor products of states in spectral Schmidt modes, whose photon-number statistics obey a geometric distribution. We study the spectral and temporal coherence properties of these states and show that their spectral coherence can be tuned---from perfect coherence to complete incoherence---by adjusting the pump spectral width. In the limit of a cw pump, these states are tensor products of true thermal states, but with different temperatures at each frequency. This could be an interesting state of light for investigating the interplay between spectral, temporal, and photon-number coherences.Comment: 6 pages main text, 1 full-page figure (12 pages total including reference and appendices

    The importance of individual heterogeneity in the decomposition of measures of socioeconomic inequality in health: An approach based on quantile regression

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    This paper shows how recently developed regression-based methods for the decomposition of health inequality can be extended to incorporate individual heterogeneity in the responses of health to the explanatory variables. We illustrate our method with an application to the Canadian NPHS of 1994. Our strategy for the estimation of heterogeneous responses is based on the quantile regression model. The results suggest that there is an important degree of heterogeneity in the association of health to explanatory variables which, in turn, accounts for a substantial percentage of inequality in observed health. A particularly interesting finding is that the marginal response of health to income is zero for healthy individuals but positive and significant for unhealthy individuals. The heterogeneity in the income response reduces both overall health inequality and income related health inequality.Health inequalities, unobserved heterogeneity, quantile regression

    Middle Darriwilian conodont zones in the uppermost San Juan limestone and the lower member of the Las Aguaditas formation, central Precordillera of San Juan, Argentina

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    The geological province of Precordillera is located in western Argentina. It extends 450 km meridionally and 110 km from east to west (Fig. 1) (Furque and Cuerda, 1979). The Lower Paleozoic stratigraphy is characterized by a thick succession of Cambro-Ordovician limestones, which were deposited in platform environments and interdigitate with clastic slope deposits toward the west (Keller et al., 1993; Astini, 1995).Fil: Feltes, Nicolás Alexis. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Museo de Paleontología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Albanesi, Guillermo Luis. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Museo de Paleontología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; ArgentinaFil: Bergström, S. M.. Ohio State University; Estados Unido

    Self-calibrating tomography for multi-dimensional systems

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    We present a formalism for self-calibrating tomography of arbitrary dimensional systems. Self-calibrating quantum state tomography was first introduced in the context of qubits, and allows the reconstruction of the density matrix of an unknown quantum state despite incomplete knowledge of the unitary operations used to change the measurement basis. We show how this can be generalized to qudits, i.e. d-level systems, and provide a specific example for a V-type three-level atomic system whose transition dipole moments are not known. We show that it is always possible to retrieve the unknown state and process parameters, except for a set of zero measure in the state-parameter space.Comment: Revised version. 9 pages, 3 figure

    'Getting out of the closet': Scientific authorship of literary fiction and knowledge transfer

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    Some scientists write literary fiction books in their spare time. If these books contain scientific knowledge, literary fiction becomes a mechanism of knowledge transfer. In this case, we could conceptualize literary fiction as non-formal knowledge transfer. We model knowledge transfer via literary fiction as a function of the type of scientist (academic or non-academic) and his/her scientific field. Academic scientists are those employed in academia and public research organizations whereas non-academic scientists are those with a scientific background employed in other sectors. We also distinguish between direct knowledge transfer (the book includes the scientist's research topics), indirect knowledge transfer (scientific authors talk about their research with cultural agents) and reverse knowledge transfer (cultural agents give scientists ideas for future research). Through mixed-methods research and a sample from Spain, we find that scientific authorship accounts for a considerable percentage of all literary fiction authorship. Academic scientists do not transfer knowledge directly so often as non-academic scientists, but the former engage into indirect and reverse transfer knowledge more often than the latter. Scientists from History stand out in direct knowledge transfer. We draw propositions about the role of the academic logic and scientific field on knowledge transfer via literary fiction. We advance some tentative conclusions regarding the consideration of scientific authorship of literary fiction as a valuable knowledge transfer mechanism.Comment: Paper published in Journal of Technology Transfe

    Non-Hermitian engineering for brighter broadband pseudothermal light

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    We show that non-Hermitian engineering can play a positive role in quantum systems. This is in contrast to the widely accepted notion that optical losses are a foe that must be eliminated or, at least, minimized. We take advantage of the interplay between nonlinear interactions and loss to show that spectral-loss engineering can relax phase-matching conditions, enabling generation of broadband pseudothermal states at new frequencies. This opens the door for utilizing the full potential of semiconductor materials that exhibit giant nonlinearities but lack the necessary ingredients for achieving quasi-phase matching. This in turn may pave the way for building on-chip quantum light sources.Comment: 11 pages (6 pages main text); 4 figure

    Entanglement reduction induced by geometrical confinement in polymer thin films

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    We report simulation results on melts of entangled linear polymers confined in a free-standing thin film. We study how the geometric constraints imposed by the confinement alter the entanglement state of the system compared to the equivalent bulk system using various observables. We find that the confinement compresses the chain conformation uniaxially, decreasing the volume pervaded by the chain, which in turn reduces the number of the accessible inter-chain contact that could lead to entanglements. This local and non-uniform effect depends on the position of the chain within the film. We also test a recently presented theory that predicts how the number of entanglements decreases with geometrical confinement.Comment: 28 pages, 10 figure

    Branching rate expansion around annihilating random walks

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    We present some exact results for branching and annihilating random walks. We compute the nonuniversal threshold value of the annihilation rate for having a phase transition in the simplest reaction-diffusion system belonging to the directed percolation universality class. Also, we show that the accepted scenario for the appearance of a phase transition in the parity conserving universality class must be improved. In order to obtain these results we perform an expansion in the branching rate around pure annihilation, a theory without branching. This expansion is possible because we manage to solve pure annihilation exactly in any dimension.Comment: 5 pages, 5 figure
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