Graphical calculus for Gaussian pure states

We provide a unified graphical calculus for all Gaussian pure states, including graph transformation rules for all local and semi-local Gaussian unitary operations, as well as local quadrature measurements. We then use this graphical calculus to analyze continuous-variable (CV) cluster states, the essential resource for one-way quantum computing with CV systems. Current graphical approaches to CV cluster states are only valid in the unphysical limit of infinite squeezing, and the associated graph transformation rules only apply when the initial and final states are of this form. Our formalism applies to all Gaussian pure states and subsumes these rules in a natural way. In addition, the term "CV graph state" currently has several inequivalent definitions in use. Using this formalism we provide a single unifying definition that encompasses all of them. We provide many examples of how the formalism may be used in the context of CV cluster states: defining the "closest" CV cluster state to a given Gaussian pure state and quantifying the error in the approximation due to finite squeezing; analyzing the optimality of certain methods of generating CV cluster states; drawing connections between this new graphical formalism and bosonic Hamiltonians with Gaussian ground states, including those useful for CV one-way quantum computing; and deriving a graphical measure of bipartite entanglement for certain classes of CV cluster states. We mention other possible applications of this formalism and conclude with a brief note on fault tolerance in CV one-way quantum computing.Comment: (v3) shortened title, very minor corrections (v2) minor corrections, reference added, new figures for CZ gate and beamsplitter graph rules; (v1) 25 pages, 11 figures (made with TikZ

Ultracompact Generation of Continuous-Variable Cluster States

We propose an experimental scheme that has the potential for large-scale realization of continuous-variable (CV) cluster states for universal quantum computation. We do this by mapping CV cluster-state graphs onto two-mode squeezing graphs, which can be engineered into a single optical parametric oscillator (OPO). The desired CV cluster state is produced directly from a joint squeezing operation on the vacuum using a multi-frequency pump beam. This method has potential for ultracompact experimental implementation. As an illustration, we detail an experimental proposal for creating a four-mode square CV cluster state with a single OPO.Comment: 4 pages, 1 figure; v2 improved discussion of the implications of our result; added discussion of finite squeezing effect

Deriving the respiratory sinus arrhythmia from the heartbeat time series using Empirical Mode Decomposition

Heart rate variability (HRV) is a well-known phenomenon whose characteristics are of great clinical relevance in pathophysiologic investigations. In particular, respiration is a powerful modulator of HRV contributing to the oscillations at highest frequency. Like almost all natural phenomena, HRV is the result of many nonlinearly interacting processes; therefore any linear analysis has the potential risk of underestimating, or even missing, a great amount of information content. Recently the technique of Empirical Mode Decomposition (EMD) has been proposed as a new tool for the analysis of nonlinear and nonstationary data. We applied EMD analysis to decompose the heartbeat intervals series, derived from one electrocardiographic (ECG) signal of 13 subjects, into their components in order to identify the modes associated with breathing. After each decomposition the mode showing the highest frequency and the corresponding respiratory signal were Hilbert transformed and the instantaneous phases extracted were then compared. The results obtained indicate a synchronization of order 1:1 between the two series proving the existence of phase and frequency coupling between the component associated with breathing and the respiratory signal itself in all subjects.Comment: 12 pages, 6 figures. Will be published on "Chaos, Solitons and Fractals

Quantum Computing with Continuous-Variable Clusters

Continuous-variable cluster states offer a potentially promising method of implementing a quantum computer. This paper extends and further refines theoretical foundations and protocols for experimental implementation. We give a cluster-state implementation of the cubic phase gate through photon detection, which, together with homodyne detection, facilitates universal quantum computation. In addition, we characterize the offline squeezed resources required to generate an arbitrary graph state through passive linear optics. Most significantly, we prove that there are universal states for which the offline squeezing per mode does not increase with the size of the cluster. Simple representations of continuous-variable graph states are introduced to analyze graph state transformations under measurement and the existence of universal continuous-variable resource states.Comment: 17 pages, 5 figure

The Highly Miniaturised Radiation Monitor

We present the design and preliminary calibration results of a novel highly miniaturised particle radiation monitor (HMRM) for spacecraft use. The HMRM device comprises a telescopic configuration of active pixel sensors enclosed in a titanium shield, with an estimated total mass of 52 g and volume of 15 cm$^3$. The monitor is intended to provide real-time dosimetry and identification of energetic charged particles in fluxes of up to 10$^8$ cm$^{-2}$ s$^{-1}$ (omnidirectional). Achieving this capability with such a small instrument could open new prospects for radiation detection in space.Comment: 17 pages, 15 figure

Gender-based violence in Public Health: challenges and achievements

Este texto trata da violência contra mulheres (VCM) como objeto científico e prático da Saúde. É uma reflexão teórica crítica concernente a processos históricos que permitem ver tanto as convergências como os afastamentos entre a tomada dessa violência como questão e particularidades do campo da Saúde, produzindo conquistas e desafios atuais em especial para a Saúde Coletiva. O texto debate aspectos interdisciplinares desse objeto científico e suas implicações para a produção do conhecimento e para as ações em saúde. Considerando as distintas culturas científicas e práticas da Saúde e outros campos que já lidam com VCM, mostram-se tensões existentes entre a perspectiva da violência como questão da saúde e como fenômeno sociocultural, ampliadas com o acréscimo da abordagem de gênero. Produzem-se então desafios de diálogo entre esses campos em termos de paradigmas, modelos científicos e linguagens de cada qual; as necessidades de intervenção social em cada campo; e a relação distinta que cada um possui entre conhecimentos e intervenção social. De outro lado, mostram-se como convergências entre esses campos as conquistas relativas aos direitos humanos e sociais e a proposta de saúde integral. Conclui-se com algumas possíveis respostas aos desafios.This text deals with violence against women (VAW) as a scientific and practical object of Health. It is a theoretical and critical reflection related to historical processes that show convergences and distances between the approach of this violence as an issue and the health field particularities, creating contemporary conquests and challenges especially to Public Health. The text debates interdisciplinary aspects of this scientific object and some impacts to the knowledge production and to health actions. Considering the different scientific and practical cultures of Health and other fields that already deal with VAW, existing tensions between health perspective and violence as a socio-cultural phenomenon are showed, becoming critical when added the gender approach. Challenges are then created on dialogs between those fields in terms of: paradigms, scientific models and languages of each one; social intervention needs in every field; and the distinct relation between knowledge and social intervention presented in each field. On the other hand, the conquests related to human and social rights and the proposal of integral health are shown as convergences between these fields. To conclude, some possible answers to the challenges are considered

Universal Quantum Computation with Continuous-Variable Cluster States

We describe a generalization of the cluster-state model of quantum computation to continuous-variable systems, along with a proposal for an optical implementation using squeezed-light sources, linear optics, and homodyne detection. For universal quantum computation, a nonlinear element is required. This can be satisfied by adding to the toolbox any single-mode non-Gaussian measurement, while the initial cluster state itself remains Gaussian. Homodyne detection alone suffices to perform an arbitrary multi-mode Gaussian transformation via the cluster state. We also propose an experiment to demonstrate cluster-based error reduction when implementing Gaussian operations.Comment: 4 pages, no figure

Cosmological quantum entanglement

We review recent literature on the connection between quantum entanglement and cosmology, with an emphasis on the context of expanding universes. We discuss recent theoretical results reporting on the production of entanglement in quantum fields due to the expansion of the underlying spacetime. We explore how these results are affected by the statistics of the field (bosonic or fermionic), the type of expansion (de Sitter or asymptotically stationary), and the coupling to spacetime curvature (conformal or minimal). We then consider the extraction of entanglement from a quantum field by coupling to local detectors and how this procedure can be used to distinguish curvature from heating by their entanglement signature. We review the role played by quantum fluctuations in the early universe in nucleating the formation of galaxies and other cosmic structures through their conversion into classical density anisotropies during and after inflation. We report on current literature attempting to account for this transition in a rigorous way and discuss the importance of entanglement and decoherence in this process. We conclude with some prospects for further theoretical and experimental research in this area. These include extensions of current theoretical efforts, possible future observational pursuits, and experimental analogues that emulate these cosmic effects in a laboratory setting.Comment: 23 pages, 2 figures. v2 Added journal reference and minor changes to match the published versio

Spectral Analysis of a Four Mode Cluster State

We theoretically evaluate the squeezed joint operators produced in a single optical parametric oscillator which generates quadripartite entangled outputs, as demonstrated experimentally by Pysher et al. \cite{pysher}[Phys. Rev. Lett. 107, 030505 (2011)]. Using a linearized fluctuation analysis we calculate the squeezing of the joint quadrature operators below threshold for a range of local oscillator phases and frequencies. These results add to the existing theoretical understanding of this potentially important system.Comment: 4 pages, 6 figure

Entanglement, recoherence and information flow in an accelerated detector - quantum field system: Implications for black hole information issue

We study an exactly solvable model where an uniformly accelerated detector is linearly coupled to a massless scalar field initially in the Minkowski vacuum. Using the exact correlation functions we show that as soon as the coupling is switched on one can see information flowing from the detector to the field and propagating with the radiation into null infinity. By expressing the reduced density matrix of the detector in terms of the two-point functions, we calculate the purity function in the detector and study the evolution of quantum entanglement between the detector and the field. Only in the ultraweak coupling regime could some degree of recoherence in the detector appear at late times, but never in full restoration. We explicitly show that under the most general conditions the detector never recovers its quantum coherence and the entanglement between the detector and the field remains large at late times. To the extent this model can be used as an analog to the system of a black hole interacting with a quantum field, our result seems to suggest in the prevalent non-Markovian regime, assuming unitarity for the combined system, that black hole information is not lost but transferred to the quantum field degrees of freedom. Our combined system will evolve into a highly entangled state between a remnant of large area (in Bekenstein's black hole atom analog) without any information of its initial state, and the quantum field, now imbued with complex information content not-so-easily retrievable by a local observer.Comment: 16 pages, 12 figures; minor change